1 International Journal of Behavioral Development # 2005 The International Society for the 2005, 29 (1), Study of Behavioural Development DOI: / The relevance of delivery mode and other programme characteristics for the effectiveness of early childhood intervention Henk Blok, Ruben G. Fukkink, Eveline C. Gebhardt, and Paul P. M. Leseman University of Amsterdam, The Netherlands Although it is generally believed that early intervention programmes are an effective means to stimulate children s cognitive development, many questions remain concerning programme design and delivery. This article reviews 19 studies into the effectiveness of early intervention programmes published from 1985 onward. The database comprised 85 different outcomes or effect sizes (71 in the cognitive domain, 14 in the socioemotional domain). The overall effect size estimate was d ¼ 0.32 (SE ¼ 0.05) in the cognitive domain, and d ¼ 0.05 (SE ¼ 0.02) in the socioemotional domain. Effect sizes were found to depend on delivery mode. Centre-based interventions and interventions following the combined home- and centre-based delivery mode produced greater effect sizes than did home-based programmes in the cognitive domain, but not in the socioemotional domain. The programme inclusion of coaching of parenting skills was also positively related to outcomes in the cognitive domain. Several other programme characteristics, including age of onset, programme length and intensity, continuation after kindergarten, and the inclusion of social or economic support, appeared not to be uniquely related to outcomes. Introduction It is generally believed that early intervention enhances the opportunities of children who are socioeconomically or culturally disadvantaged. Many independent studies have contributed to the belief that early intervention is effective. The comprehensive reviews carried out by Lazar and Darlington (1982) and McKey, Condelli, Ganson, Barrett, McConkey, and Plantz (1985) marked the end of years of dispute over the effectiveness of early intervention for disadvantaged children. Since then, the perspective on early intervention has broadened. More comprehensive approaches have been advocated, encouraging a combination of different service delivery formats, the inclusion of additional parent components, and the longer duration of programmes, by starting them at an early age and continuing them after kindergarten. More specifically, four related issues pertain to the required comprehensiveness of early intervention to achieve long-term effects on the development of disadvantaged children. First, there has been a growing awareness in the field that effective programmes should target both the child and the parents to promote stable effects on the child s development. Some programmes have combined a child-focused, centrebased approach with a parent-focused, home-based approach to reach this goal, while others have adopted either a specific home-based or a specific centre-based approach. The second issue, which is related to the first, is the question which parentfocused components yield additional benefits for the development of children. Some programmes include a component that is focused on parenting skills, whereas others offer the parents social and economic support. The third issue concerns the timing: When should a programme begin, and when should it end? These three issues, all of which pertain to the required comprehensiveness of early intervention programmes, have been specifically linked in recent discussions to the effects of early intervention in the long termwhich is the fourth and final issue. Furthermore, although the interest in cognitive gains from early intervention has not diminished, it is now complemented with the study of socioemotional outcomes. We discuss these four themes below in the context of the conceptual framework developed by Ramey and Ramey (1998) as a way of introducing our research questions. This frameworkwhich is called biosocial developmental contextualismderives from social ecology, developmental systems theory, and developmental neurobiology, and addresses the principles of effective early intervention. Delivery format of programmes Biosocial developmental contextualism clarifies that there are multiple pathways in early intervention to improve children s development. Programmes may influence the parents or provide direct educational experiences to children, or they may do both. Three corresponding programme types are distinguished: home-based, centre-based, and a combination of home- and centre-based delivery. Correspondence should be sent to Henk Blok, University of Amsterdam, Faculty of Social and Behavioral Sciences, SCO- Kohnstamm Instituut, Wibautstraat 4, 1091 GM Amsterdam, The Netherlands; This research was supported by a grant from the Netherlands Organization for Scientific Research (NWO), contract Interested readers may obtain the search profiles (used in ERIC and PsychINFO) and the complete data matrix from the first author.
2 36 BLOK ET AL. / EFFECTIVENESS OF EARLY CHILDHOOD EDUCATION Home-based interventions rely on an indirect way of stimulating children s development (e.g., through parent training). A common starting point of home-based programmes is the belief that the parents of disadvantaged children use less effective parenting strategies because they lack the necessary knowledge (Goodson, Layer, StPierre, Bernstein, & Lopez, 2000). It is hypothesised that home-based programmes lead to a change in parental attitudes, behaviour, and school involvement. This results in more and higherquality parent child transactions and family-orchestrated child experiences (Guralnick, 1998), and these have positive effects on the child. However, reviews of the available evidence for the effects of home-based programmes are not too optimistic (Gomby, Culross, & Behrman, 1999). Parenting intervention alone is viewed as too weak, because parenting beliefs and practices cannot be altered easily (Halpern, 2000). Other authors have concluded that although home-based programmes can affect parental attitudes and behaviour, such programmes do not result in positive child outcomes (Farran, 2000). Centre-based programmes provide children with direct educational experiences, for instance in a daycare or preschool setting. Findings in this field have shown that significant effects can be achieved for developmental competence and achievement tests at the end of preschool and into kindergarten. There is growing evidence that direct provision in centre-based approaches is more effective than indirect provision in homebased approaches (Barnett, 1995; Bowerman, Donovan, & Burns, 2001; Farran, 2000; McGuire & Earls, 1991; Ramey & Ramey, 1998). Ramey and Ramey clearly favour a centrebased approach, as they are convinced that the direct provision of learning experiences leads to larger and more enduring benefits than does indirect provision (e.g., parent training). Several programmes offer a combination of home-based and centre-based components. Combining the two delivery formats may create more pathways for positive change in families lives and have synergetic effects (Smith & Zaslow, 1995). Surprisingly, however, the seemingly widely shared preference for a combined approach is not unequivocally supported by reviews. While in their narrative reviews Barnett (1995) and Farran (2000) favour a combined approach, White, Taylor, and Moss (1992) found no convincing evidence that the involvement of parents results in more effective outcomes. White et al. reviewed eight studies of disadvantaged children in which the degree of parental involvement represents the only difference between the experimental groups. The average effect size for all studies across all child measures was 0.11 of a standard deviation, with the best designed studies arriving at the weakest results. To conclude, there are still unanswered questions concerning the effectiveness of these service delivery models, as noted by Campbell and Ramey (1995, p. 745). Programme comprehensiveness Biosocial developmental contextualism promotes a more inclusive view of early intervention (Ramey & Ramey, 1998). The field of early intervention has moved on from a specific focus on the deficits of the child to, in more recent programmes, a focus on both child and family. Many of these programmes include a component that focuses on the coaching of parenting skills. Other programmes also offer the parents social and economic support. The promotion of child development, the enhancement of parenting skills, and the provision of adult services can also be combined in a threepronged approach. A principal issue is which goals deserve primary attention in early intervention. Reynolds (1998), for example, argues that although there is consensus about the importance of providing comprehensive services, there is less consensus about the relative importance of these services and the extent to which these services should be provided (p. 508). For example, it can be hypothesised that the coaching of parenting skills, which can be conceived as an indirect but targeted approach to stimulate the development of children, is more beneficial to children than adult economic or social support, which is primarily focused on the parents. Furthermore, it is an open question whether interventions that are theoretically powerful are also more effective in practice (Gomby, Larner, Stevenson, Lewit, & Behrman, 1995). Timing and duration of programmes Research in developmental neurobiology has recently underlined the importance of very early stimulation. It is becoming increasingly clear that neurodevelopment is for a large part experience-driven, and that brain development depends on early experiences (Shore, 1997). This motivates an early start of interventions that aim at the improved development of disadvantaged children. Halpern (2000) has stressed that intervention should not only start early, but also be continuous in order to be effective in the long run. Farran (2000) and Rimm-Kaufman and Pianta (2000) specifically emphasised the importance of the transition from kindergarten to primary school, which evokes the need for continued support. According to Reynolds (1998), early intervention should be continued into second or third grade in order to promote long-term effectiveness. Retention of effects The above-mentioned issues of multiple combined formats, the inclusion of additional components, and the timing and duration of programmes have been specifically discussed in the context of the long-term effectiveness of early intervention (Barnett, 1995; Gomby et al., 1995; Reynolds, 1998). Basically, there are two hypotheses concerning the outcome of early intervention. The first predicts that the immediate effects are sustained. The cognitive advantage hypothesis, for instance, predicts that early intervention initiates a positive cycle of scholastic development and commitment that culminates in improved developmental outcomes in adolescence and beyond (Reynolds, Mavrogenes, Bezruczko & Hagemann, 1996, p. 1119). However, the second, rival hypothesis predicts that effects fade over time. Farran (2000), for example, emphasised that most programmes focus on concrete skills related to readiness tests, whereas profound curricular changes take place in third and fourth grade. Several evaluations have indeed shown a fading of the positive results (Blok & Leseman, 1996; McKey et al., 1985). Significant effects of centre-based programmes, for example, are rare byand nonexistent beyondfirst grade, according to Farran (2000) and Gilliam and Zigler (2000). The increasing number of studies and the longer span of follow-up studies enable not only a more precise, but also a more general estimate of the retention of programme effects in the long run.
3 INTERNATIONAL JOURNAL OF BEHAVIORAL DEVELOPMENT, 2005, 29 (1), Goal of the study The goal of the study was to answer questions regarding the delivery and design of early intervention programmes for disadvantaged children. The inclusion of additional programme components, and the timing, duration, and intensity of programmes were among the design features. We also paid attention to the recency of programmes. Finally, we distinguished between the immediate effects of the programme and their retention. Effectiveness is defined at the child level, distinguishing between cognitive and socioemotional effects. To answer these questions, we conducted a meta-analysis of the outcomes published from 1985 onward. We decided to restrict ourselves to this year of publication because many earlier results had already been reviewed (in, e.g., Lazar & Darlington, 1982; McKey et al., 1985; White et al., 1992). Method Selecting the studies We searched ERIC and PsychINFOthe major databases in the fields of education and child developmentcombining three groups of descriptors: one to indicate the independent variables (e.g., programme evaluation, curriculum evaluation, course evaluation, home programmes, parent training, daycare), one to indicate the dependent variables (e.g., outcomes of education, basic skills, academic achievement, cognitive development), and one to indicate the age of the students (e.g., early childhood education, preschool education, kindergarten, toddler). We thus focused explicitly on programmes with an educational orientation, excluding programmes oriented solely toward socioemotional development or child health. We also excluded studies of gifted children and of children who are at risk for medical reasons (e.g., premature birth, handicapped, impaired, retarded, disabled). All selected studies appeared to focus on disadvantaged children. The references of collected papers and articles were searched for additional references. Additionally, relevant studies were suggested by experts. We deliberately restricted our search to articles published in peer-reviewed journals. The rationale was that limiting studies to those passing the test of peer review minimises the risk of admitting studies of poor quality. For the same reason, studies had to include a nontreated control group in order to qualify for our analysis. Our final set comprised 19 studies, which were subsequently subjected to the review procedure. Deciding on the relevant comparisons There was not always a simple one-to-one correspondence between studies and experimental comparisons, namely comparisons between an experimental and a control group. Some studies reported the effects of more than one experimental condition, while others evaluated essentially the same experimental condition in more than one sample. On the other hand, one and the same experimental comparison was differentially conceived of in different publications, for instance when one article reported on the full sample, and a subsequent articleevaluating follow-up resultsreported on only a subsample of the original sample. We therefore decided to adopt the level of the experimental comparison as the unit of coding. Relatively straightforward decisions could be taken for several studies, whereas decisions were more complicated in the case of others. Kagitcibasi, Sunar, and Bekman (2001) reported effects of the Turkish Early Enrichment Projectan adaptation of the Hippy (Home Instruction Program for Preschool Youngsters) programme, which was originally developed in Israel (Lombard, 1981). They complemented it with a mother training component. Their study was a factorial design with three categories of early childhood care (preschool, daycare, homecare), two levels of home intervention (Hippy, no Hippy), and two age levels (3 and 5 years at the beginning of the study). Because the number of students in the different cells was rather low, we decided to aggregate the data by age levels. Furthermore, we considered the Hippy/no Hippy factor as our main factor of interest. Accordingly, the study allowed us to make three comparisons, namely the effect of Hippy/no Hippy in three early childhood care arrangements: preschool, daycare, and homecare. The results of generic Head Start programmes have been reported by Lee, Brooks-Gunn, and Schnur (1988) and Lee, Brooks-Gunn, Schnur, and Liaw (1990). In both articles, participation in Head Start was compared to either no preschool or other preschool experiences, allowing two comparisons (Head Start vs. no preschool, and Head Start vs. other preschool). The first article provided data from pretests and posttests, the latter administered immediately after the end of the intervention. The second article reported no pretest results, but only posttests results 1 and 2 years after the end of the Head Start intervention. Although the samples overlapped considerably, they were not identical: The sample dealt with in the follow-up article was 33% smaller (the Head Start group had shrunk from 414 to 333, the no-preschool group from 390 to 204, and the other preschool group from 165 to 109), excluding all non-black children. We decided to combine the results of both articles, noting that the results of the follow-up measures might be biased. Madden, Slavin, Karweit, Dolan, and Wasik (1993) and Slavin, Madden, Karweit, Livermon, and Dolan (1990) reported outcomes of Success for All (SFA), an intervention programme starting in preschool and continuing into Grade 3. Slavin et al. described the first year of SFA (1987/1988), and reported outcomes for five samples (preschool, kindergarten, Grade 1, Grade 2, Grade 3). Only the first two samples were relevant to our review, as the other samples had received no early intervention. The results reported in Madden et al. concerned outcomes from the third year of SFA (1990/1991), by which time the programme was running in five different schools. Some of these outcomes (collected at the Abbottston school) were regarded as follow-up results for the students in the 1987/1988 sample. Other outcomes reflected independent data gathered from other schools. We extracted four comparisons from the two articles: two concerning Abbottston data (including follow-up results in 1990/1991) and two reflecting Grade 1 (evaluating the effect of preschool and kindergarten intervention, aggregated by school) and Grade 2 (evaluating the effect of kindergarten only, also aggregated by school, but excluding Abbottston), respectively. These comparisons were defined in this way to avoid an overlap in the sample of students. The outcomes of the Abecedarian project have been reported in many journal articles, beginning with Burchinal, Lee and Ramey (1989). The research design changed in the course of the project, and finally consisted of three experi-
4 38 BLOK ET AL. / EFFECTIVENESS OF EARLY CHILDHOOD EDUCATION mental conditions and one control condition. Two experimental comparisons were within the domain of our research question. One was that between the CC (control condition, i.e., no preschool, no follow-up programme) and the EE condition, in which students received preschool education for the first 5 years of their life, followed by a supplementary Educational Support Program from kindergarten through 2nd grade. The second comparison we extracted from the available data was that between the CC condition and the EC condition, in which students received only the preschool programme and not the follow-up programme. The data we used came from Ramey, Campbell, Burchinal, Skinner, Gardner, and Ramey (2000), who presented IQ data from 5 to 15 years old, and school performance data from 8 to 15 years old. The results of the Chicago Child-Parent Center and Expansion Program (CPC&EP) have also been widely represented in the research literature. We selected the outcomes reported in Reynolds (1994) as our reference data, because the presented intervention groups were the most relevant to our research question. We extracted one experimental comparison from these data, namely the full intervention group with follow-on (denoted as PS þ KG þ PG-3 by Reynolds) with the non-cpc comparison group. We found two studies on the effectiveness of a supplementary emergent literacy curriculum compared to a standard Head Start programme (Whitehurst, Epstein, Angell, Payne, Crone, & Fishel, 1994; Whitehurst, Zevenbergen, Crone, Schultz, & Velting, 1999). The second study is a replication of the first, and includes a follow-up of both the original cohort and the replication cohort. Unfortunately, the outcomes of the two studies were not reported independently, as the second article (Whitehurst et al., 1999) combined the results of both cohorts. This left us no choice but to use the outcomes of the second article only, as it concerned the biggest sample and provided follow-up results. The two Whitehurst et al. studies therefore resulted in one experimental comparison, namely Head Start with an emergent literacy add-on contrasted with a Head Start-only condition. After all decisions had been made, there remained 34 experimental comparisons. Coding of variables The experimental comparisons in the database were coded for several characteristics (see Table 1). Variables 1 3 concern design characteristics, variables 4 11 concern sample characteristics, and variables concern characteristics of the experimental intervention. Because most experimental comparisons resulted in multiple outcomes, other variables (variables 18 25) were coded at Table 1 Coding scheme for the experimental comparisons, and reliability of coding Inter-coder Variable Scale reliability a 1. Subject assignment 0. Strictly controlled (randomisation or matching at subject level); 1. no strict control 87 (randomisation or matching at group level, post hoc comparison, or no control at all) 2. Treatment fidelity 0. High in most respects; 1. unknown Intervention in control group 0. Standard programme, not under control of experimenter; 1. unknown programme 92 or no programme at all 4. Nation 0. USA; 1. other than USA Recency of programme Numerical (minus 1900).93 b (year implementation started) 6. Size of experimental group Number of students 1.00 b 7. Size of control group Number of students.99 b 8. Mean age of students at onset of study Number of months (before birth coded as 0).96 b 9. Percentage of students from ethnic Percentage.96 b minorities 10. Level of education of parents 1. Low; 2. mixed; 9. unknown Level of income of parents 1. Low; 2. mixed; 9. unknown Delivery mode 1. Home-based; 2. centre-based; 3. combination of home- and centre-based Length of programme Number of months (a year equals 10 months, unless otherwise indicated by.99 b experimenter) 14. Intensity of programme Number of hours per week.91 b 15. Continuation after K 0. No; 1. yes Inclusion of social or economical 0. No; 1. yes 85 support 17. Inclusion of coaching of parenting skills 0. No; 1. yes Effect size at pretest Numerical 1.00 b 19. Standard error of pretest effect size Numerical.94 b 20. Domain of the posttest 0. Cognition 1. socioemotional development Time of measurement of posttest Number of months after intervention ended, coded on a time scale of years 1.00 b 22. Type of posttest score 0. Observed score; 1. gain score or score adjusted for covariates Type of posttest effect size 0. Derived by reviewers; 1. reported by experimenters Effect size at posttest Numerical 1.00 b 25. Standard error of posttest effect size Numerical.94 b a Percentage of classifications agreed upon by the two coders, unless otherwise indicated. b Product moment correlation between the codes of the two coders.
5 INTERNATIONAL JOURNAL OF BEHAVIORAL DEVELOPMENT, 2005, 29 (1), the level of effect sizes. Hedges unbiased estimate d was used as an effect size estimate (variables 18 and 24). This statistic uses the within-group standard deviation as a method of standardisation. It includes a correction factor to obviate bias resulting from small samples. The standard error of the effect size (variables 19 and 25) was estimated following Hedges and Olkin (1985, p. 86, Eq. 15). Whenever possible, we used observed scores to calculate effect sizes. Several experimenters, however, reported only gain scores or scores adjusted for covariates, indicated by variable 22 (type of posttest score). Some reported outcomes were inherently negative, for instance when behaviour ratings referred to negative behaviour. In these cases, outcomes were recoded simply by changing the sign. This correction procedure was applied to the studies by Goodson et al. (2000), Johnson and Walker (1987), Scarr and McCartney (1988), and Seitz, Rosenbaum, and Apfel (1985). Two independent coders coded all the studies. Inter-coder reliability was estimated by determining the rate of agreement in the case of a nominal scale, or the product moment correlation in the case of an interval scale. The results are reported in the last column of Table 1. The reliability proved to be satisfactory, ranging between 85 and 100% for nominal variables, and between.91 and 1.00 for interval variables. In the case of divergent codes, final codes were established by mutual agreement, and used in subsequent analyses. Many study designs either did not incorporate a pretest or did not report sufficient statistics to estimate an effect size that captured the initial differences between conditions at the pretest. We were able to determine pretest effect sizes for only 40% of our cases. To prevent an excessive loss of data, we decided to impute zero scores for missing effect sizes at pretesting. This value is close to the mean value we found for cases, which allowed us to estimate a pretest effect size (mean value 0.06 with a corresponding standard error of 0.04). Integration of effects The coding phase resulted in a file containing 207 different outcomes (171 in the cognitive domain, 36 in the socioemotional domain) from the 34 experimental comparisons. We analysed the data in two steps. We first aggregated effect sizes to the level of the experimental comparisons. This aggregation was performed separately for each domain and time of measurement, varying from 0 to 180 months after the intervention ended. This aggregation was conducted by weighted integration, in which the results were weighted in inverse proportion to their standard error (i.e., the greater the standard error, the smaller the weight). The aggregated effect sizes and the corresponding standard errors were estimated following Hedges and Olkin (1985, p. 112, Eqs. 8 and 9). This aggregation model assumes the results within one study to be homogeneous and to differ from each other only on the basis of random differences between the outcome variables. The standard errors of aggregated effect sizes are generally smaller than the standard errors corresponding to the constituent effect sizes, which seems a fair reward for using more than one outcome measure. All calculations on aggregations were done using the Meta programme (Schwarzer, 1989). This first step resulted in 85 different outcomes (71 in the cognitive domain, 14 in the socioemotional domain). As a second step, outcomes or effect sizes were integrated into an overall effect size, separately for each domain. The integration was performed according to the random effects model (Hedges & Olkin, 1985). The model we specified acknowledges the hierarchical and longitudinal nature of our data. The model splits the effect size d ijt for experimental comparison j from study i at moment t into two components, namely a true effect size d ijt, and an error component e ijt. The true effect sizes are assumed to vary across measurement moments t, comparisons j, and studies i. The variance of d ijt is explained by the regression model: d ijt ¼ g 0 þ g n Z nijt þ u ijt þ v ij þ w i (1) where g 0 is the grand mean, Z nijt are characteristics of the studies (n being the index referring to the characteristics), comparisons and measurement moments, and u ijt,v ij, and w i are residual error terms at the three levels distinguished. The model makes it possible to distinguish between three variance components, viz. s 2 u (the variance between measurement moments t), s 2 v (the variance between experimental comparisons j ), and s 2 w (the variance between studies i ). The model also enables testing whether any of the parameter variances are significantly different from zero with the test statistic Q. If study outcomes are heterogeneous, it is worthwhile trying to relate the heterogeneity to the various characteristics Z nijt.if not, the study outcomes are homogeneous and no explanatory variables need to be introduced in equation (1). The specification and testing of models was carried out with MLwiN, using restricted maximum likelihood estimation (Goldstein et al., 1998; Hox, 2002). Analyses were performed separately for both domains (cognition, socioemotional development). Results Description of the studies in the database This subsection briefly describes the studies in our database, which yielded 34 different comparisons (Table 2). Assignment of the subjects to the different conditions of the comparison proceeded according to strict guidelines (at random, by matching, or by blocking) in only 16 cases. In other cases, less strict procedures were followed (e.g., random assignment or matching of intact groups), or assignment was not under the control of the investigator. Treatment fidelity was reported to be high in all or most respects for 11 of the 34 comparisons. For the other comparisons, no information could be found. However, this does not necessarily mean that the treatment was jeopardised. We found the same lack of information with respect to the control condition. Students in the control condition mostly followed a standard programme. The sample size was generally small, averaging 77 for both the experimental and the control conditions. This average excludes the outlying large sample size of the study by Goodson et al. (2000), which featured about 1600 children in both conditions. The experimental group contained more than 100 students in only 8 of the 34 comparisons. Evidently, such small sample sizes imply generally low power to detect a difference in outcomes. Most students belonged to an ethnic minority group (average: 81%, taking experimental and control groups together). Median student age at the start of the intervention programme showed considerable variation, ranging from pre-birth to 64 months (average 37 months). Both the socioeconomic status and the income of parents were
6 40 BLOK ET AL. / EFFECTIVENESS OF EARLY CHILDHOOD EDUCATION Table 2 Summary of characteristics of the studies in the meta-analysis Variables References Experimental comparisons Baker et al., Cohort I (Hippy vs. Control) Cohort II (Hippy vs. Control) Gersten et al., Direct instruction (K-3) vs Comparison Goodson et al., Comprehensive Child Development Program vs. Control Howell et al., Peabody LDK-R vs. Control Boehm RG vs. Control Bracken CDP vs. Control Johnson & Walker, 1987, Houston Parent Child Development ; Walker & Johnson, Program vs. Control Kagitcibasi et al., Education daycare (ED) with mother training (MT) vs. ED without MT Custodial daycare (CD) with mother training (MT) vs. CD without MT Home care (HC) with (MT) vs. HC without MT Lee et al., 1988; Head Start vs. No preschool Head Start vs. Other preschool Olds et al., 1994; Treatment 3 vs. Treatment (1 þ 2) Olds et al., Treatment 4 vs. Treatment (1 þ 2) Slavin et al., 1990; Success for All (SFA) preschool Madden et al., /1988 vs Control SFA kindergarten 1987/1988 vs. Control SFA grade /1991 vs. Control SFA grade /1991 vs. Control Ramey et al., Abecedarian (preschool þ K-2 transition) vs. Control Abecedarian (preschool only) vs. Control Reynolds, Chicago CPC and EP (full intervention) vs. Non-CPC comparison group Riksen-Walraven et al., Instapje vs. Control Scarr & McCartney, Mother Child Home Program vs. Control Schweinhart, 2000; Perry Preschool vs. Control Luster & McAdoo, Schweinhart et al., Distar vs. Control High/Scope vs. Control Nursery vs. Control Seitz et al., Family Support Intervention vs. Control Tuijl et al., Hippy vs. Control (Moroccan sample) Hippy vs. Control (Turkish sample) Wasik et al., Care þ Family Education vs. Control Family Education vs. Control Whitehurst et al., Head Start þ Emergent Literacy Intervention vs. Head Start See Table 1 for explanation of variables and codes. generally low. On average, 76 and 97%, respectively, of the parents were classified in the lowest category. Of the 34 comparisons, 26 were conducted in the United States, 3 in the Netherlands, 3 in Turkey, and 2 in Bermuda. The comparisons were more or less uniformly distributed with regard to the delivery mode: 13 concerned a home-based programme, 11 a centre-based programme, and 10 a combined home- and centre-based programme. Because delivery mode was pertinent to our research question, the following section provides a more detailed discussion of the programmes concerned. Most comparisons were of programmes that included the coaching of parenting skills (29 out of 34). Social or economic support was much less frequently included in the comparisons (6 out of 34). The duration of the programmes varied greatly, viz. from 4 to 96 months (average: 22 months). The intensity of the programmes varied from 1 to 25 hours per week (average: 8.5 hours per week). Most programmes were discontinued when students entered Grade 1, or earlier. Only five comparisons concerned programmes that were continued after kindergarten; all these were centre-based or a combination of homebased and centre-based.
7 INTERNATIONAL JOURNAL OF BEHAVIORAL DEVELOPMENT, 2005, 29 (1), Description of programme types As mentioned in the Method section, we classified the early intervention programmes into three different programme types, namely home-based, centre-based, and a combination of home- and centre-based. Each of these programme types is discussed below, and each programme included in the review is briefly mentioned in order to provide a glimpse of the variety of programmes. Home-based programmes. Thirteen of the comparisons concerned home-based interventions. Of these, seven concerned a programme based on Hippy (Lombard, 1981). Baker, Piotrkowski, and Brooks-Gunn (1998) provided two comparisons based on a US Hippy programme, Kagitcibasi et al. (2001) provided three comparisons based on a Turkish Hippy adaptation, and Van Tuijl, Leseman, and Rispens (2001) provided two comparisons based on a redesign of a former Dutch Hippy adaptation. All Hippy-like programmes focused on parents as the instructors of their children, using paraprofessionals recruited from the parents community to instruct and support the parents, and professional coordinators to organise parent group-meetings. Programmes started when children were between 4 and 5 years old, and lasted for 2 years (effectively 30 weeks per year). Each year, home visits were made and group meetings were held every other week. Over the course of the programme, parents received a series of books written specifically for the Hippy programme, along with activity packets, to which the parents were introduced during the home visits and group meetings. The packages focused on language, problem-solving, and sensory skills, and were aimed at better preparing the children for school. The Comprehensive Child Development Program (CCDP) (Goodson et al., 2000) is a two-generation programme that employed case management and home visiting to provide multirisk, low-income children and their parents with a range of education, health, and social services. The programme served participating families until the child entered kindergarten or first grade. Most CCDP projects used home visits to deliver early childhood education for children between birth and the age of 3 years. The visits, which were made every 2 weeks, were focused on the parentseducating them about child development and teaching parenting skillsrather than on providing services directly to children. Olds et al. (1998; Olds, Henderson, & Kitzman, 1994) evaluated the effects of a programme of prenatal and early childhood home visitation by nurses. The programme was intended to avert preterm delivery and low birthweight, and in the postpartum phasedevelopmental delays and behavioural problems. The nurses helped the women to improve their health-related behaviours and the quality of their infant care-giving. Families in treatment group 3 were provided with home visiting services during pregnancy only, while families in treatment group 4 received the same services until the child s second birthday. Instapje was a Dutch, parent-focused home-based programme (Riksen-Walraven, Meij, Hubbard & Zevalkink, 1996) aimed at improving the quality of parental support in families from deprived socioeconomic backgrounds. The programme was relatively short, consisting of 16 weekly home-visits only, starting when the child was 13 months old. Parents were supported on four behavioural dimensions: providing emotional support, respecting the child s autonomy, structuring and limiting the child s environment, and supporting language development. The programme materials consisted of a manual for the mothers and a set of play materials to be used with the child. The Mother Child Home Program (MCHP), implemented with Bermudan families, was the subject of the study by Scarr and McCartney (1988). It was a widely used US early childhood programme that employed home visitors to demonstrate to mothers different ways of interacting with their children (2- to 4-year-olds). The 2-year programme consisted of home visits made every other week. One of the key goals was to teach mothers to be effective teachers. Wasik, Ramey, Bryant, and Sparling (1990) reported on the effectiveness of a family education intervention programme designed... to help the parent foster the cognitive and social development of the child (p. 1686). The programme called for regular home visits (weekly for the first 3 years, and then less frequently), starting a month after the child s birth and continuing throughout the preschool years. Home visitors discussed ongoing concerns with parents and offered problemsolving strategies to cope with difficult situations. Centre-based programmes. Eleven of our comparisons concerned centre-based interventions, each of which involved a more or less specific school curriculum. Gersten, Darch, and Gleason (1988) evaluated a direct instruction curriculum, Howell et al. (1990) evaluated three preschool language curricula, Lee et al. (1988, 1990) evaluated generic Head Start programmes, Slavin et al. (1990) and Madden et al. (1993) evaluated SFA, and Reynolds (1994) evaluated the CPC&EP. Most of these curricula were continued into the first three grades, with the exception of the preschool language curricula evaluated by Howell et al. and the Head Start programmes evaluated by Lee. The sample Lee was concerned with consisted of children who had attended preschool in 1969/ 1970, which makes their evaluation valid only for Head Start as it existed about 30 years ago. Furthermore, all children in the Howell et al. study (i.e., both those in the experimental groups and those in the control group) received Head Start, the main difference between the groups being the supplementary language curriculum they received. The other programmes in the centre-based category were based on the idea that early intervention programmes should be continued in the early grades. The direct instruction programme evaluated by Gersten et al.which focused on integrating cognitive with social developmentstarted in kindergarten, using specific teaching materials. The authors stressed that most of the academic content was taught through games and other forms of informal social interaction. However, they were less clear about the direct instruction programme in Grades 1 to 3. The SFA programme has been described in detail by Slavin et al. and Madden et al. SFA comprised half-day preschool and full-day kindergarten programmes, with a heavy emphasis on language and reading. Readiness activities included the use of the Peabody Language Development Kit, which the Howell et al. study also included. The reading programme in Grades 1 to 3 included regrouping students into homogeneous reading groups, increasing direct instruction time, and using reading tutors to provide one-to-one instruction. Each participating school favoured a family support team, providing parenting education and encouraging parents to support their children s
8 42 BLOK ET AL. / EFFECTIVENESS OF EARLY CHILDHOOD EDUCATION success with learning. Similar to the SFA programme, the CPC&EP represented a large-scale comprehensive preschool to Grade 3 intervention (Reynolds, 1994). This centre-based programme was designed to improve children s development through structured instructional support services, parental involvement, and emphasising reading and language development. The children involved in the experimental comparison were in the programme for 5 years, namely from preschool through Grade 3. The preschool component was a structured half-day programme for 3- and 4-years-olds, and was designed to promote children s prereading and language skills and socioemotional development through reduced class size, parental involvement, staff training, and structured learning activities. From kindergarten onward, the programme was a full-day programme, with similar goals and approaches. Parental involvement was realised by requiring parents to invest at least half a day per week in the school. Parents could choose from a wide range of activities, such as serving as classroom aides, tutoring children, performing clerical tasks, or accompanying classes on field trips. Combined home- and centre-based programmes. Ten of the comparisons concerned an intervention that combined elements of a home- and a centre-based approach. These interventions represented a wide variation of arrangements. The Houston Parent Child Development Center (Johnson & Walker, 1987, 1991; Walker & Johnson, 1988) was designed to promote social and intellectual competence in general, and to prevent behaviour problems and school failure in particular. The programme required 550 hours of participation over a 2- year period, starting with 1-year-old children. The first year of the programme took place in the home and focused on the mother child interaction. Mother and child came to the project centre during the second year to participate with other families in classes on child-rearing skills and other topics related to family life. The family support intervention evaluated by Seitz et al. (1985) provided a wide range of services to parents and their children. These services included social work, pediatric care, daycare, and psychological services. The programme began during the mother s pregnancy and continued for 30 months after birth. Daycare was provided for most of the period and was of high quality. The staff was highly trained, and the child caregiver ratio was three to one. Home visitors coordinated the services provided and visited the families on average 28 times during the programme. The well-known Abecedarian programme was the subject of the evaluation reported by Ramey et al. (2000). Two comparisons were included in our database, namely of the children who received the preschool programme only, and the children who received the preschool and the school-age programme (i.e., kindergarten through Grade 2 educational support). Although some of the services provided were parentdirected, the focus of the Abecedarian preschool programme was on centre-based child education. Children participated in the preschool programme from the age of 6 weeks until they were 5 years old. The childcare centre was of high quality by common standards, and provided year-round, full-day care. Parents were provided with a programme on parenting topics, but no home visits were made. The school-age programme (from kindergarten through Grade 3) featured, in addition to the regular school curriculum, home/school resource teachers who tried to enhance parental involvement. Twice a week, teachers provided parents with home curriculum activities individually designed for each child in order to reinforce his or her academic development. Children in the Perry Preschool Study (Schweinhart, 2000) followed a specifically designed cognitively oriented curriculum that lasted 2 years, starting at age 3. Children participated in morning classes, 5 days a week. The staff child ratio was one adult for every five or six children. Each week, the teachers made a 90-minute home visit to the families, during which they reviewed classroom activities and discussed similar activities in the home. The study by Schweinhart, Weikart, and Larner (1986) resulted in three comparisons, concerning the DISTAR and the High/Scope programme, and a traditional nursery programme. The programmes differed with respect to the degree of initiative expected of the child and the teacher, but shared two components, viz. half-day classroom sessions and educational home visits. A teacher visited each mother and child at home every two weeks. During these visits, the teacher tried to engage the mother in learning activities with the child, paralleling the approach used in the classroom. The programmes lasted for 2 years, starting when the children were 3 years old. Project CARE was modelled on the Abecedarian project (Wasik et al., 1990). In one of the conditions in the study by Wasik et al., CARE was combined with the Family Education programme (which was briefly described in the section on home-based interventions). Within CARE, children were offered high-quality, full-day daycare. Curriculum materials emphasised both the cognitive and the socioemotional domain. Daycare attendance started when the children were just a few months old, and continued until they entered kindergarten. The intervention programme evaluated by Whitehurst et al. (1999) was a regular Head Start programme supplemented with an emergent literacy component. The intervention consisted of two components, namely (1) an interactive book-reading programme for children at home, and at school based on the principles of dialogic reading, and (2) a phonemic awareness curriculum only offered at school. Both parents and teachers were taught how to read dialogically. The phonemic awareness curriculum was carried out in the second half of the school year. The intervention encompassed the preschool year, when children were on average 4 years old. The intervention took about 1 2 classroom hours per week, plus presumably the same amount of time at home. Results of the meta-analysis Table 3 gives a first impression of the effect sizes at posttesting within the domains distinguished. Median effect sizes amounted to 0.44 for the cognitive domain and to 0.01 for the socioemotional domain. There was one outlier, corresponding to a value of This effect size stems from the study by Schweinhart et al. (1986) and concerns the difference in the cognitive domain between the DISTAR group and the control group, assessed directly after the end of the treatment. Because follow-up assessments 12, 24, 36, and 60 months later revealed consistently large effect sizes, we rejected the possibility of a simple error. It was decided to retain this outcome in the data file. Applying multilevel regression analysis, it appeared that the variance component at the highest level (i.e., that of the study) was generally very small and was not statistically different from
9 INTERNATIONAL JOURNAL OF BEHAVIORAL DEVELOPMENT, 2005, 29 (1), Table 3 Stem-and-leaf display of effect sizes at posttesting (rounded to one decimal), including numbers and medians Stem Cognitive domain Domain/leaf Socioemotional development Number Median zero in either domain. We therefore decided to remove this level from our models. Table 4 presents the results for the twolevel models without the inclusion of predictor variables. The integrated effect size is estimated at 0.32 (SE ¼ 0.05, p 5.05) for the cognitive domain, which is between a small and a medium effect as defined by Cohen (1988). The integrated effect size for the socioemotional domain is very small at 0.05 (SE ¼ 0.02, p 5.05). The variance components at both levels were also rather small, indicating that the variance of the outcome measures was largely a result of error variance. However, the test of homogeneity indicated for both domains that part of the variance was systematic. In an effort to reduce the variability of the outcomes, most of the coded variables (except variables 19, 20, 24 and 25; see Table 1) were introduced into the equation as predictors. The categorical variable delivery mode (variable 12) was recoded into dummy variables. Additionally, an extra predictor variable was composed by multiplying the length of the programme (variable 13) by the intensity of the programme (variable 14). This new variable Dose represents more or less the total intervention effort. Characteristics of the outcome measures, experimental comparisons, and studies were progressively Table 4 Parameter estimates for the start model without predictors in two domains Cognitive domain (n ¼ 71) Socioemotional development (n ¼ 14) Parameters Coeff. SE Coeff. SE Fixed effects Integrated effect size 0.32* * 0.02 Random effects Variance between experimental comparisons Variance between times of measurement 0.06* 0.03* Test of homogeneity Q ¼ *, df ¼ 70 Q ¼ 80.87*, df ¼ 13 * Effects statistically different from zero (p 5.05). entered as predictors, starting with the characteristic that showed the strongest association, and proceeding with the next best predictor. The addition of characteristics was halted when no predictor could be found that significantly decreased the heterogeneity of the effect sizes. This search for predictors was performed separately for both domains. The resulting models were considered to be the final ones (Table 5). Both models appeared to be stable, as a back-tracking procedure (starting with all possible predictors and progressively deleting the weakest predictor) led to the same results. The final models for the cognitive and the socioemotional domain both contained some unexplained variance, as indicated by the test of homogeneity. However, none of the variance components was statistically different from zero, as they were smaller than twice their standard errors. The interpretation of the regression coefficients is relatively straightforward, because the coefficients were not standardised and dichotomous variables were coded as either 0 (characteristic not present) or 1 (characteristic present). In the cognitive domain, the regression weights for the dummy variables for the centre-based and the combined home- and centre-based delivery indicated an advantage of about 0.4 to 0.5 SD over home-based programmes. In the socioemotional domain, only a small negative effect could be demonstrated for home-based programmes. However, this effect of 0.05 SD is not significantly different from zero. One other single programme characteristic turned up as a significant predictor: programmes that included the coaching of parenting skills had a positive effect on outcomes in the cognitive domain (of about 0.7 SD), but not in the socioemotional domain. Three other significant predictors in the cognitive domain represented characteristics of the study design. Using a control group following no programme at all (or following an unknown programme) increased the results by about 0.25 SD. Using gain scores or a design with covariates decreased the results by, again, 0.25 SD. Positive effect sizes at pretesting were associated with higher effect sizes at posttesting. Finally, the time of measurement exerted a small, but significant, negative effect of 0.03 (SE ¼ 0.01) on outcomes in the cognitive domain, indicating that, on average, effect sizes diminished by 0.03 SD for each consecutive year. This effect might be interpreted as a representation of the fading of outcomes over time. Discussion Early intervention programmes generally tend to be moderately effective in the cognitive domain, but not in the socioemotional domain. The raw overall effect size was equal to 0.3 SD in the cognitive domain and to nearly zero in the socioemotional domain. Two programme characteristics were found to be related to outcome measures, but only in the cognitive domain: the delivery mode and the inclusion of the coaching of parenting skills. Home-based programmes were about 0.5 SD less effective than both centre-based programmes and combined home- and centre-based programmes. The inclusion of parenting skills support had a particularly strong effect on outcomes (0.7 SD). Several other programme characteristicsincluding programme recency, programme length, programme intensity, total programme dose, children s age at programme onset, continuation of programme after
10 44 BLOK ET AL. / EFFECTIVENESS OF EARLY CHILDHOOD EDUCATION Table 5 Parameter estimates for the final model in two domains Cognitive domain (n ¼ 71) Socioemotional development (n ¼ 14) Parameters Coeff. SE Coeff. SE Fixed effects Integrated effect size Intervention in control group (Var. 3) Dummy centre-based (Var. 12) a Dummy combined home-/centre-based (Var. 12) a Dummy home-based (Var. 12) a Inclusion of coaching of parenting skills (Var. 17) Effect size at pretest (Var. 18) Time of measurement (Var. 21) Type of posttest score (Var. 22) Random effects Variance between experimental comparisons Variance between times of measurement 1.02* 0.24* 0.48* 0.42* 0.69* 0.63* 0.03* -0.22* * Test of homogeneity Q ¼ *, df ¼ 63 Q ¼ 76.64*, df ¼ 12 indicates parameter not specified. See Table 1 for the interpretation of the variables. a The variable delivery mode (Var. 12) was replaced by dummy variables. * Effects statistically different from zero (p 5.05). kindergarten, and provision of social or economic support to parentsshowed no relationship with outcome measures. Further, the longitudinal nature of the available outcome measures allowed us to estimate the fading of outcomes after ending of interventions. This effect amounted to 0.03 SD per year. Finally, effect sizes were also moderated by three study design characteristics, namely whether or not the control group had followed a standard programme, the difference between the experimental and the control group at pretesting, and the use of gain scores rather than observed scores. The results of our meta-analysis confirm quantitatively the conclusions reached in narrative syntheses regarding the considerably stronger efficacy of centre-based programmes or combined centre- and home-based programmes in the cognitive domain (Barnett, 1995; Bowerman et al., 2001; Farran, 2000; McGuire & Earls, 1991; Ramey & Ramey, 1998). The results show that the outcomes of these programmes are about 0.5 SD larger than those of home-based programmes. The overall effectiveness of early intervention programmes with an educational orientation appeared to be near zero in the socioemotional domain. The results of this study do not confirm the particular importance of a combined intervention for obtaining effects in this domain as well (Yoshikawa, 1994). Our analyses revealed no evidence of a unique contribution to programme outcomes of age of onset, duration, intensity and dose of the programme, or forms of parental and family support, with the exception of the provision of parenting skills. This seems to contradict conclusions resulting from previous narrative syntheses (Barnett, 1995; Bryant & Maxwell, 1997; McGuire & Earls, 1991), and those presented in quantitative reviews (Leseman, Otter, Blok, & Deckers, 1998; Royce, Darlington, & Murray, 1983) and as theoretical considerations (Rutter, 2000). A possible explanation for this is that in these other studies, which focused mostly on bivariate relationships, there may have been confounding between these programme characteristics and the delivery format. Recency of the programme, onset age, and programme duration appeared not to be significantly related to the delivery mode. However, centre-based and combined home- and centre-based programmes were on average much more intensive, and therefore provided a clearly higher dose of intervention than home-based programmes did. Correlations of a dummy variable denoting centre-based and combined home- and centre-based programmes versus home-based programmes with intensity amounted to.76 (p 5.001) and with dose to.47 (p 5.01). Therefore, the importance of programme intensity and programme dose may be masked, at least partly, by delivery mode. No effect of the continuation of the preschool intervention into elementary school was found in addition to the effect of basic delivery strategy, which seems to contradict in particular the rather robust findings of three major studies included in the present analysis, namely those concerning the CPC&EP, the preschool plus K2 version of the Abecedarian project, and the extensions of the SFA programme into the lower grades. From a theoretical perspective, enhancing continuity upon transitions between the most important social contexts of the young child (i.e., home, preschool, and elementary school) seems very important to optimise developmental and learning gains (Rimm-Kaufman & Pianta, 2000). Again, confounding with delivery strategy may be a possible explanation for the lack of such effect in the present meta-analysis. No home-based programme in the present selection was continued after kindergarten or transferred into the first grade of elementary school. This notwithstanding, however, it seems a distinct possibility that the previously reported significance of continuing preschool interventions into elementary school holds only for the particular programmes for which this effect has been found.
11 INTERNATIONAL JOURNAL OF BEHAVIORAL DEVELOPMENT, 2005, 29 (1), In summary, centre-based and combined centre- and homebased programmes were on average characterised by a higher intensity and thus a higher dose of the intervention than were home-based programmes, and they also appeared to be more often continued into elementary school. These three features were related to programme efficacy in previous narrative reviews. As we could estimate models in which all predictors were included, we found delivery mode to be the better predictor, leaving no room for unique contributions from other programme characteristics, except the inclusion of parenting coaching. Particularly important in the present results was the additional strong effect of including the coaching of parenting and parenting skills, which was found to increase the effect size in the cognitive domain by 0.7 SD. The studies reviewed did not provide detailed information on how parenting coaching and parenting skill training affected programme outcomes. Therefore some possible mechanisms will be briefly discussed here. Several studies have pointed to the importance of an emotionally supportive home environment for cognitive gains from education in preschool and kindergarten (Pianta, Nimetz, & Bennett, 1997; van IJzendoorn, Sagi & Lambermon, 1992). What seems to be crucial is the child s trust in social relationships, which transfers from the home to the centre or school. Parenting coaching in the included programmes may have improved emotional support in the family and attachment to others (Van Tuijl & Leseman, 2004). A different explanation is that programmes with parenting coaching have effectively counteracted the frequently reported problems with programme implementation in highrisk groups, varying from irregular attendance to the reluctance of parents to participate in parental activities or to work with the child at home (Farran, 2000). This may explain why the coaching of parents to provide the support needed (e.g., bringing children to the centre on time, well-rested, and wellnurtured; attending parent teacher conferences) is associated with positive child outcomes. In contrast to the effect of parenting skills training, no such effect was found for the inclusion of a social, health, or economic family support component. Note, however, that this type of parent and family support may yield important effects in other outcome measures, such as the long-term prevention of child abuse and neglect (MacLeod & Nelson, 2000), and the prevention of health problems, emotional problems, and conduct disorders in adolescence (Olds et al., 1998; Olds & Kitzman, 1993). Although these outcomes may not be directly relevant to short-term cognitive or socioemotional goals, they may modulate in particular the preservation of early effects up into adulthood and their transformation into life-phaserelevant outcomes, such as social adjustment, economic independence, and positive health behaviour (Yoshikawa, 1994). Programme effects do fade over time. Our results confirm previous observations of this phenomenon and have resulted in a robust quantitative estimate. The mean linear decrease of the effect size based on the nine studies that reported medium long-term and long-term follow-up results, covering all types of programmes, was estimated at 0.03 SD per year, which is less than previously reported (Blok & Leseman, 1996; McKey et al., 1985). Based on this, it would take 10 years for an immediate programme effect of d ¼ 0.3 (the average effect found in this study) to completely disappear. According to McKey et al., who based their conclusions on Head Start evaluation studies conducted before 1982, this would be about 2 years. Our selection included more studies with long-term follow-up measurements than previous reviews did, even up to 15 years after withdrawing the intervention (Olds et al., 1998). An important consideration is that the decrease in effect size may be nonlinear, with a stronger decrease in the first few years after the intervention, but a less strong decrease in subsequent years, as hypothesised by Ramey et al. (2000). Many more long-term outcomes will be needed to test this hypothesis. Few studies in the present meta-analysisfocusing on programmes with an educational orientationreported outcomes in the socio-emotional domain. This finding, which may be related with our search and selection strategy, seems to reflect the predominant cognitive orientation of early childhood intervention programmes, despite the growing recognition of the strong interrelatedness of motivation, emotionally based self-regulation, and cognitive learning in education programmes (Barnett, Young, & Schweinhart, 1998; Boekaerts, 1999). The selected studies that did include socioemotional outcome measures revealed a much smaller overall effect size than was found for cognitive outcomes. However, no strong negative effects were reported in the studies we investigated, in contradiction to the results of Haskins (1985) on early centre-based education programmes with a strong cognitive emphasis, and to the recent findings of the Early Childcare Network of the National Institute of Child Health and Human Development (NICHD) regarding intensive, early-onset centre-based care (NICHD, 2002). Nonetheless, the observation that early intervention programmes with an educational orientation do not seem to have an impact on the socioemotional development is worrying, given the interrelatedness of motivational, emotional, and cognitive processes in post-intervention school learning. The competition between socioemotional and cognitive-academic goals is also at the heart of the debate on developmentally appropriate versus didactic practices in early childhood education (Marcon, 1999; Schweinhart & Weikart, 1997; Stipek, Feiler, Daniels, & Milburn, 1995). Our study does not indicate programme design characteristics that are related to socioemotional outcomes for early intervention programmes with an educational orientation. This leaves us with the question how future programmes of this type should be designed to achieve positive effects in the socioemotional domain. An interesting programme characteristic in this respect may be the programmes pedagogical processes (e.g., child-centred versus teacher-directed, developmental versus didactic curriculum). As noted earlier, the programme design characteristics explored here do not fully explain the variation in effect sizes. The process characteristics alluded to here are obvious candidates to explain the still unexplained variation in outcomes. Unfortunately, few studies provide sufficient details about the daily processes and teacher child interactions to determine the impact of different pedagogical models on cognitive and socioemotional outcomes. Finally, our results have two more or less clear implications regarding the format or delivery of future programmes. The findings provide a strong argument for the delivery of programmes in a centre or a combined centre- and homebased format. Furthermore, the findings suggest to include a parenting skills component, although this probably will only affect the cognitive development of children, but not their socioemotional abilities. It is difficult to formulate further implications with regard to programme intensity and length, continuation after kindergarten, and the target age of children,
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