1 JOURNAL OF EDUCATION FOR STUDENTS PLACED AT RISK, 11(2), Copyright 2006, Lawrence Erlbaum Associates, Inc. Early Childhood Intervention and Educational Attainment: Age 22 Findings From the Chicago Longitudinal Study Suh-Ruu Ou and Arthur J. Reynolds Institute of Child Development University of Minnesota-Twin Cities This study investigated whether participation in the Chicago Child-Parent Center (CPC) Preschool Program associated with higher educational attainment (high school completion, highest grade completed, and college attendance) at age 22. The study sample included 1,334 youth (869 in the preschool group and 465 in the comparison group) from the Chicago Longitudinal Study. Probit regression was used to examine the group differences in educational attainment controlling for child and family characteristics, including gender, race/ethnicity, and family risk status. Results indicated that CPC preschool participation was significantly associated with more years of education (11.33 vs , p<.001), a higher rate of high school completion (Diploma or General Equivalency Diploma [GED], 66.9% vs. 55.3%, p <.001), and a higher rate of college attendance (23.0% vs. 17.9%, p =.055). Only gender subgroups showed an interaction effect with program participation on high school completion among all subgroups. Males benefitted more from the preschool program than females on high school completion. Findings demonstrate that largescale school-based programs can have enduring effects into early adulthood. Early childhood education is a preventive intervention for economically disadvantaged children. The goal of such programs is to improve disadvantaged children s skills so that they can begin school on an equal footing with their more advantaged peers. Early childhood education programs offer learning opportunities beyond Correspondence should be addressed to Suh-Ruu Ou, Chicago Longitudinal Study, 222A Child Development, Institute of Child Development, University of Minnesota-Twin Cities, 51 East River Road, Minneapolis, MN
2 176 OU AND REYNOLDS those available to children in their families and in other natural childcare environments, and they often include social and health services and parent educational components. Many programs have demonstrated short-term benefits. However, only a few studies have followed up to age 20 or beyond. The present study examined long-term effects of the Chicago Child-Parent Center (CPC) Preschool Program on educational attainment at age 22. Two research questions are addressed: RQ1: Is participation in the CPC preschool program associated with higher educational attainment? RQ2: Which subgroups benefit most from the CPC program participation? LONG-TERM EFFECTS OF EARLY INTERVENTION PROGRAMS The positive associations between early intervention programs and school competence and achievement have been found in many studies (Barnett, 1995; Barnett, Young, Schweinhart, 1998; Bryant & Maxwell, 1997; Campbell, Pungello, Miller-Johnson, Burchinal, & Ramey, 2001; Ensminger & Slusarcick, 1992; Reynolds, Mavrogenes, Bezruczko, & Hagemann, 1996; Reynolds, Temple, Robertson, & Mann, 2001). Findings have suggested that such programs are effective in increasing the probability that a child completes high school (Oden, Schweinhart, & Weikart, 2000; Reynolds, et al., 2001). In addition, results from several model programs have shown positive longterm effects. Follow-up studies in the Abecedarian Project showed significant associations between program participation and outcomes such as: higher reading and mathematic achievement test scores, fewer grade retentions, more years of education, and greater likelihood to attend a 4-year college (Campbell et al., 2001; Campbell, Helms, Sparling, Ramey, 1998; Campbell & Ramey, 1995; Ramey et al., 2000). Follow-up studies in the High/Scope Perry Preschool Programs showed that the preschool group had higher school achievement, a higher rate of high school graduation, more years of education, and higher adult earnings up to age 27 (Barnett et al., 1998; Schweinhart, Barnes, & Weikart, 1993; Schweinhart & Weikart, 1983, 1997). Findings from the CPC Program, a large-scale publicly funded program, indicated significant associations between program participation and higher school achievement, a lower rate of grade retention at age 15, and a lower dropout rate and a higher high school completion rate at age 20 (Reynolds, 2000; Reynolds et al., 2001; Reynolds, Ou, & Topitzes, 2004; Temple, Reynolds, & Miedel, 2000). Findings from other large-scale Head Start programs have not been consistent. Some studies have shown significant associations between program participation and
3 EARLY INTERVENTION AND EDUCATIONAL ATTAINMENT 177 outcomes such as: lower rates of grade retention and higher rates of high school graduation (Oden et al., 2000; Seitz, Apfel, Rosenbaum, & Zigler, 1983). However, some studies found the significant associations faded out 1 or 2 years after the program (Currie & Thomas, 1995, 2000; Lee & Loeb, 1995; McKey et al., 1985; Westinghouse Learning Corporation, 1969). Garces, Thomas, and Currie (2002) found that participation in Head Start is associated with higher rates of high school completion and college attendance for Whites but not for African Americans. More evidence regarding impacts on educational attainment from large-scale programs is needed. DIFFERENTIAL EFFECTS FOR SUBGROUPS Along with questions about main effects of early intervention programs, some researchers have examined whether the associations differ for subgroups of children. The subgroups typically examined include gender, racial/ethnic membership, socioeconomic level, and parental education (Barnett et al., 1998; Gray, Ramsey, & Klaus, 1983; Lally, Mangione, & Honig, 1988; Oden et al., 2000; Reynolds, 2000; Reynolds et al., 2001; Schweinhart & Weikart, 1983; Schweinhart et al., 1993; Seitz et al., 1983). However, there are no consistent findings that one subgroup of children benefited more from programs than others. Among those subgroup analyses, gender was examined most frequently, and other subgroups were examined in only a few studies. Some studies found that magnitudes of associations between participation in early intervention programs and school related outcomes were larger or lasted longer for females than for males (Barnett et al., 1998; Beller, 1983; Campbell, Ramey, Pungello, Sparling, & Miller-Johnson, 2002; Gray et al., 1983; Lally et al., 1988; Oden et al., 2000), but Reynolds et al. (2001) found that associations between program participation and high school dropout rates were larger for males. Magnitudes of associations on nonschool outcomes, such as arrests and earnings, were larger for males than for females in some studies (Schweinhart et al., 1993; Reynolds et al., 2001). Other studies, however, found no difference in magnitudes of associations by gender (Campbell et al., 1998; Lazar, Darlington, Murray, Royce, & Snipper, 1982; Royce, Darlington, & Murray, 1983). Overall, there are no consistent findings in relation to gender subgroups. Some Head Start studies found that associations were stronger for the lowest socioeconomic groups (Oden et al., 2000). Campbell et al. s (1998) findings suggested parental education levels and risk levels could be used as subgroup categories. However, findings from the Consortium for Longitudinal Studies and the CPC Program showed no different magnitudes of associations among children with different background characteristics, such as two- versus one-parent family
4 178 OU AND REYNOLDS and different levels of mother s educational attainment (Reynolds, 2000; Royce et al., 1983). Although researchers were concerned about differential magnitudes of associations for subgroups, they had difficulty conducting subgroup analyses due to small sample sizes. METHOD Sample and Data The study sample consisted of children participating in the Chicago Longitudinal Study (CLS, 1999), an ongoing investigation of the life-course development of a panel of low-income minority children growing up in high-poverty neighborhoods in Chicago. The original sample (N = 1,539) included 989 children who entered the program in preschool and graduated from kindergarten in from 20 CPCs, and 550 children (a comparison group) who came from 5 randomly selected schools in the Chicago Effective Schools Project (27 schools in low-income neighborhoods were identified by school districts as in need of improving students test scores and basic performance) with kindergarten intervention programs in without CPC preschool experience. Because they were living in Title I-eligible neighborhoods, all children in this cohort were eligible for and participated in government-funded early childhood programs. In addition, in enrolling in full-day kindergarten programs, some children in the comparison group (N = 85) participated in the Head Start preschool enrichment program, so the comparison group provides a good contrast in exploring the effects of CPC participation relative to participation in the usual educational treatment. Continuously promoted children graduated from high school in The sample in the present study included 1,334 youth (86.7% of the original sample) for whom educational attainment could be determined by May 2002 (M age = 22.0). This sample included 87.9% of the original CPC preschool group and 84.6% of the comparison group. Students in and outside of the Chicago Public Schools were identified. Among high school completers (diploma or General Equivalency Diploma; GED), 70.8% graduated from schools in Chicago. Among high school graduates (diploma only), 89.3% graduated from school in Chicago, and 82.8% graduated from Chicago Public Schools. Data were collected from a variety of sources, such as youth, parents, teachers, and school administrative records. Table 1 shows the similarity of the study sample (N = 1,334) attributes for the preschool group and the comparison group at the time of program entry or as soon afterwards as possible. Attributes include background information, such as gender, race/ethnicity, family risk index by child s age 8, parents educational attainment, and family structure. The p-values for the original sample are provided for comparison between the original sample and the study sample.
5 EARLY INTERVENTION AND EDUCATIONAL ATTAINMENT 179 TABLE 1 Characteristics of Preschool Group and Comparison Group a Characteristics N Chicago Child Parent Center Preschool Group b No- Preschool Group c P-value Original Sample p-value Percentage females 1, *.100 Percentage Black 1, Family risk index (0-6) by child s age 8 1, Percentage either parent completed high 1, *.036* school at child s age 8 d Percentage single parent by child s age 8 d 1, Percentage parent not employed by 1, * child s age 8 d Percentage ever reported receiving free 1, lunch by child s age 8 d Percentage having 4 or more children at 1, **.002* home d Percentage children in school area in 1, *.037* which 60% or more of children reside in low-income families Percentage of low-income families in 1, school region Percentage abuse/neglect report by 1, child s age 4 e Percentage parent were teen at child s birth 1, Note. The numbers for any indicated abuse or neglect from court or Department of Child and Family Services are as follows: Preschool group = 1.15%, comparison group = 2.58%, and p-value =.051. The numbers for percent either parent completed high school at child s birth are as follows: Preschool group = 62.8%, comparison group = 54.9%, and p-value =.006. a N = 1,334. b N = 869. c N = 465. d Means reported before imputation for missing data. e Data were from court. *Significant at.05 level. **Significant at.01 level. There were no significant differences between the groups in more than half of the attributes. But there were significant differences in some characteristics, such as gender, parents education, and family size. There were also significant differences in the neighborhood indicator, the percentage of children in a school area in which 60% or more of children reside in low-income families. In the original sample, there were significant differences between groups in those attributes except for gender. In the study sample, the CPC preschool group had a greater proportion of females than the comparison group, but in the original sample, numbers of females and males were evenly split. Parents were more likely to have completed high
6 180 OU AND REYNOLDS school at child s age 8 in the CPC preschool group than the comparison group, which was the same as in the original sample. The CPC preschool group had smaller average family size than the comparison group. In addition, CPC preschool group participants were more likely to live in a high-poverty neighborhood, and the parents were more likely to be not employed by child s age 8. Those differences were taken into account in the analysis. CPC Program The CPC Program is a center-based early intervention that serves 3- and 4-year-old children who come from families in high-poverty neighborhoods that are not being served by Head Start or other early intervention programs. The CPC program is designed to promote children s school competence, especially school readiness and academic achievement, and the services are from preschool to early elementary school. The components of the CPC Program include parental involvement, comprehensive services, and a child-centered focus on the development of reading/language skills (Reynolds et al., 1996; Sullivan, 1971). The comprehensive services include: (a) attending to children s nutritional and health needs (i.e., free breakfasts, lunches, and health screenings); (b) coordinated adult supervision, including a CPC head teacher, parent resource teacher, school-community representative, and a teacher aide for each class; (c) funds for centralized in-service teacher training in child development as well as instructional supplies; and (d) emphasis on reading readiness through reduced class size, reading and writing activities in the learning center, and reinforcement and feedback (Reynolds et al., 1996). Currently, the CPC program is conducted in 23 centers throughout the Chicago Public Schools. Eighteen centers are located in separate buildings close to the elementary school, and 5 are attached to the wings of the parent elementary school (Reynolds, 2000). One thing that needs to be noted is that the comparison group participated in alternative programs rather than no intervention of any kind. This introduces a conservative bias to estimates of program impact. Eligibility and Features. To be eligible for enrollment in the CPC program, children need to meet three conditions. First, children must live in school neighborhoods that receive Federal Title I funds. Second, children cannot be enrolled in another preschool program (e.g., Head Start). Third, parents must agree to participate in the program at least 1 half-day per week (Reynolds, 2000). The CPCs have three important features. First, they are part of the school system, in contrast to Head Start programs that usually link to social service or community agencies. The CPCs are in separate buildings or in wings of the affiliated elementary schools, whereas Head Start programs are located independently. Second, eligibility for the CPCs is based on neighborhood poverty, but for Head Start, eligibility is based on family-level poverty. CPCs are located in the highest poverty
7 EARLY INTERVENTION AND EDUCATIONAL ATTAINMENT 181 neighborhoods. Therefore, the participants might be more disadvantaged than the participants in other programs. Finally, the CPCs provide services for up to 6 years for children from ages 3 to 9, whereas Head Start provides preschool programs only. Therefore, the CPC program has the potential to provide a stable school environment during preschool and the early primary-grade years (Reynolds, 2000). Preschool and Kindergarten Components. The components of this program include a structured half-day preschool program for 3- and 4-year-olds, a half-day or an all-day kindergarten program for 5-year-olds, with a child-centered focus on the development of reading/language skills, literacy skills, and other family support services. The center operates on the regular 9-month school year calendar. An 8-week summer program is often provided. The program is offered in different sites; however, it has no uniform curriculum. Each site tailors its program to children s needs through a unified philosophy of literacy and a common core of activities that include individualized instruction, small group activities, and field trips. A central assumption of the program is that parental involvement is an important socializing force in young children s development. Parents are required to be involved at the center at least 1 half-day per week. Involvement may include a wide variety of activities, such as parents volunteering as classroom aides, interacting with other parents in the center s parent resource room, participating in educational workshops and courses, attending school events, accompanying classes on field trips, and attending parent-teacher meetings on behalf of the child (Reynolds, 2000; Reynolds et al., 1996). MEASURES Educational Attainment Data were obtained from administrative records in all schools youth attended and were supplemented by interviews with youths and family members. Data were also collected in schools youths were likely to attend. Three measures were used: high school completion, college attendance, and highest grade completed. High school completion. High school completion is the official measure of high school attainment status by the National Center for Education Statistics and the Census Bureau and has been the common measure used in other intervention studies. This dichotomously coded variable indicates whether youths completed their secondary education with an official diploma or were awarded a GED credential by May All others were coded as noncompleters.
8 182 OU AND REYNOLDS Although high school graduation and GED completion are counted as high school completion, between these two types of completion, there are fundamental differences, such as future earning and chances of continuing to college (Cameron & Heckman, 1993; Heckman, 2000). Therefore, they were examined as supplemental measures. High school graduation was coded dichotomously: Youths completing high school through traditional graduation were coded 1; otherwise they were coded 0. Youths who completed high school by obtaining GED were excluded rather than coded as 0 because GED is not the same as dropouts. Therefore, the sample size was 1,163. Alternative sample size (N = 1,334, GED coded as 0) was examined as well. College attendance. This dichotomously coded variable indicates whether a youth attended any college (2- or 4-year college) by May If any report showed that one attended any college, they were coded 1; otherwise, they were coded 0. The sample size was 1,315 due to missing values. Highest grade completed. Highest grade completed by participants was coded as a continuous variable, ranging from 7 to 16, and college attendance and GED attainment were taken into account in this variable. Obtaining a GED was coded 12, and college attendance was coded depending on credits earned. Thirty credits were treated as equaling one year of college attendance. For example, 30 earned credits were coded 13, and 60 earned credits were coded 14. The sample size was 1,315 due to missing values. CPC Preschool Program Participation Participation in the CPC Preschool Program for 1 or 2 years was coded 1; children who did not attend the CPC preschool program were coded 0. Covariates Covariates included race/ethnicity, gender, CPC follow-on participation, abuse/neglect by child s age 4, and family risk status. All variables except family risk status were measured as dichotomous variables. Table 2 presents the number of valid cases, age of assessment, group means, total means, and standardized deviations for the measures. The maximum valid N is 1,334, and the minimum N is 1,163 for high school graduation because GED completers were not included.
9 EARLY INTERVENTION AND EDUCATIONAL ATTAINMENT 183 TABLE 2 Descriptive Statistics for Study Variables a Variables N Age Preschool Group M Comparison Group M Total M SD Chicago Child-Parent Center 1, preschool participation Black 1, Family Risk Index * 1, Females 1, Highest grade completed 1,315 By High school completion 1,334 By High school graduation (GED 1,163 By is excluded) High school graduation (GED 1,334 By is coded as 0) GED completion 1,334 By College attendance 1,315 By Note. a N = 1,334. *Six items formed a composite index of risk. Items included were (a) single-parent family status by the child s age 8; (b) parent unemployment by the child s age 8; (c) attendance at a kindergarten program in a school in which 60% or more of children in the attendance area reside in low-income families; (d) eligibility for a subsidized lunch; (e) parent a nongraduate of high school by the child s age 8; and (f) four or more children in the household. GED = General Equivalency Diploma. Data Analysis T tests were employed with and without covariates, and then regression and probit regression were used to examine the adjusted differences between groups as a robust test. Regression was employed for highest grade completed, and probit regression was employed for dichotomous outcomes. Effect sizes (Cohen, 1988) were calculated to compare the magnitudes of effects of the CPC preschool program on indicators of educational attainment. Attrition analyses were conducted through three procedures: T tests between youth in-sample and not-in-sample, interactions of preschool participation and in-sample status, and Heckman s (1979) selection model. Probit regression was used because it provides better estimates for dichotomous variables. As with the logit regression, the probit regression is another type of statistical model for dealing with data with binary dependent variables. Probit and logit parameters are estimated by Maximum Likelihood (ML). In most applications, logit models and probit models will give identical results. However, when the distribution of dependent variables is concentrated in one tail rather than more equally distributed, estimates from logit and probit models may differ substantially (Aldrich & Nelson, 1984; Liao, 1994). Probit coefficients can be used to
10 184 OU AND REYNOLDS compute marginal effects, which denote changes in the probability of experiences of the outcome (such as high school completion) per a one-unit change in the explanatory variable, holding all other variables constant. To make sure that the difference between groups was not due to demographic factors, adjusted means were obtained by controlling different sets of covariates, starting with four covariates: gender, race, follow-on participation, and family risk index. Then the covariate abuse/neglect by age 4 was added, and other individual indicators of family risk index were used. Individual indicators of the family risk index such as parent education, free/reduced-price lunch status, single-parent family status, parent unemployment, family size, and low-income school neighborhood were used for other alternative models instead of family risk index. Differential program effects by subgroups, including gender, parent s educational attainment, family income level, and family risk status, were explored, although there were no consistent findings in previous studies. The interaction terms of program by subgroups were entered into regression models step by step, and differences in chi-square between models were examined. RESULTS Educational Attainment in the Study Sample According to the U.S. Department of Education (2004a), the national high school completion rate for all 18- to 24-years-olds in 2001 was 86.5%. The 4-year completion rate for ninth-grade public school students ( ) was 75.8% in Illinois. Both rates were higher than the rate of the study sample. At age 22, 61.8% of the study sample had completed high school. More than one-fifth of the sample (22.2%) completed more than 12 years of education. Among this group, 0.6% had a highest grade of 16 (earned a bachelor s degree); 1.5%, (15), completed more than 2 but less than 4 years of college; 0.5%, (14), earned an associate s degree or completed 2 years of college; and 19.6%, (13) completed 1 but less than 2 years of college. The distribution of the highest grade completed in this sample shows lower educational attainment than the national sample of non-hispanic Blacks reported by U.S. Department of Education (2004b). This gap is not surprising given that the CPC participants grew up in high-poverty neighborhoods. Overall, educational attainment in the study sample was lower than in the national sample and in the Black non-hispanic sample. Main Effects of the CPC Preschool Program on Educational Attainment Although the study sample had lower educational attainment than the national samples, the preschool group had a higher level of educational attainment than the
11 EARLY INTERVENTION AND EDUCATIONAL ATTAINMENT 185 comparison group. As mentioned earlier, to make sure that the differences were not due to demographic factors, adjusted means were estimated by controlling for different sets of covariates. Table 3 shows the rates of educational attainment of the two groups. Means and rates of educational attainment were used interchangeably. High School Completion and Highest Grade Completed Significant differences between the preschool group and the comparison group remained even after adjustments for different sets of demographic factors. For example, after adjusting for differences in gender, race, follow-on participation, and family risk status, the rate of high school completion for the preschool group was 66.9% and 55.3% for the comparison group, a difference of 11.6 points (p<.001; see Table 3). Similar results were found on the rates of high school graduation (61% vs. 50.4%, p <.05) and highest grade completed (11.33 vs , p <.001). College Attendance The effect of preschool participation on college attendance was not as consistent as it was on the highest grade completed and high school completion. Although unadjusted means indicate that there was a significant difference between the CPC pre- TABLE 3 Educational Attainment by Groups a Educational Attainment N Preschool Group b Comparison Group c Difference p-value % Change Over Comparison Group Effect Size d Index d High school 1, completion, % High school 1, graduation, % (GED is excluded) High school 1, graduation, % (GED is coded as 0) GED 1, Highest grade 1, completed College attendance, % of total sample 1, (1.67) 17.9 (1.77) a The rates of groups were adjusted for gender, race, follow-on participation, and family risk index. b N = 869. c N = 465. d Value was derived from Probit transformation of proportions (Cohen et al., 2002). For effect size d index,.2 indicates a small effect,.5 indicates a medium one, and.8 indicates a large effect as suggested by Cohen (1988).
12 186 OU AND REYNOLDS school group and the comparison group in college attendance (23.8% vs. 18.3%, p =.027), there were no consistently significant differences at the.05 level between groups after different sets of adjustments were made. Nevertheless, the CPC preschool group had about 5 percentage points higher rate of college attendance than the comparison group after adjustments (23% vs. 17.9%, p =.055). Subgroup Analysis Table 4 shows the rates of educational attainment by subgroups. There were significant differences in rates of high school completion among subgroups (parent education, family risk, family income level, and gender subgroups), but the interaction terms of CPC preschool participation by subgroups were not significant for all outcomes except for the interaction effect of preschool participation and gender on high school completion (B =.12, p =.030), favoring males. Preschool participation was more effective for males than for females in increasing high school completion. Because gender significantly interacted with preschool participation in relation to high school completion, a separate gender analysis was conducted to further examine the differences. Educational attainment by preschool experience and gender was examined, adjusted for race, follow-on participation, and family risk status. More males who had preschool experience completed high school than males who did not have preschool experience (61.1% vs. 41.5%, p <.001). This difference of 19.6 percentage points was much larger than for females. For females, 70.0% of those who had preschool experience completed high school, and 68.5% of those who did not have preschool experience completed high school, a difference of 1.5 points. Preschool males also had significantly higher rates of graduation (53.2% vs. 37%, p <.001) and GED (16.8% vs. 6.8%, p <.01) than comparison males. A similar result was found on highest grade completed (11.13 vs. 10.5, p <.001). One thing worth noting is that females with CPC preschool experience had a higher rate of college attendance than those without CPC preschool experience (30.9% vs. 23.0%, p =.051). Attrition Analysis Attrition analysis was conducted to determine selection bias. Following contemporary evaluation technique, a Heckman (1979) selection model was estimated using the computer software STATA 8.0 (STATA Press Staff, 2003). Two equations were estimated simultaneously; one was for in-sample status and the other was for high school completion, taking attrition into account. The procedure is used to determine whether the error terms between the two equations are significantly correlated (defined by Rho). If the errors are correlated, then there might be an unmeasured common link between attrition and educational attainment, which would
13 TABLE 4 Educational Attainment by Subgroups by Age 22 (Unadjusted) Educational Attainment N Males a M Females b M Parent Completed HS at Child s Birth c M Parent Not Completed HS at Child s Birth d M Family Risk Index Less Than 4 at Child s Age 8 e M Family Risk Index Equal or More Than 4 at Child s Age 8 f M Not Eligible for Free or Reduced Lunch at Child s Age 8 g M Eligible for Free or Reduced Lunch at Child s Age 8 h M High school % completion 1, ** ** ** ** 57.9 Graduation, % of total 1, ** ** ** ** 51.7 sample (GED is excluded) GED, % of total sample 1, Highest grade completed 1, ** ** ** ** (1.78) (1.60) (1.70) (1.71) (1.74) (1.66) (1.65) (1.73) College attendance, % of 1, ** ** ** ** 18.8 total sample College attendance, % of HS completers ** ** * 32.1 Note. Sample size for parent education is 1,273 for high school completion, and 1,255 for highest grade completed and college attendance. Standard deviances are in parentheses. a N = 652. b N = 682. c N = 765. d N = 508. e N = 526. f N = 808. g N = 370. h N = 947. *p <.05. **p <
14 188 OU AND REYNOLDS bias the estimated main effects. Selective attrition is a threat to internal validity. If the preschool and comparison groups are different, it would be hard to attribute the differences between groups to program participation. Results supported the hypothesis that the correlation between error terms of the two equations was not significantly different from 0 (See Appendix for results). Thus, there was no selective attrition in the sample for educational attainment. After taking attrition into account, the difference between groups increased slightly from 11.6 to 11.9 percentage points. Similar estimation procedures were conducted using college attendance as the outcome: The results were similar. The results from the attrition analyses showed that the attrition in the study sample was not a threat to internal or external validity. Other than Heckman s selection model, two procedures were used to examine attrition. First, the means by groups of in-sample and not-in-sample were compared for background variables, early and later achievement, and school mobility. There were no significant differences between the groups with and without known educational attainment status in terms of background and school achievement variables, such as parents status of high school completion and Iowa Test of Basic Skills word analysis at kindergarten. However, there were significant differences between groups in the percentage that were Black (p <.05), percentage that were female (p <.05), preschool participation (p <.05), follow-on participation (p <.01), number of school moves from Grades 4 to 8 (p <.01), and percent of juvenile arrests by age 18 (p <.01). In other words, the attrition group was less likely to be Black and less likely to participate in follow-on services; that is, the school-age program. In addition, the attrition group was more likely to change schools from Grades 4 to 8. Second, the interaction of preschool participation and in-sample status was used in a regression analysis with covariates to see if it was related to kindergarten achievement, family risk status at child s age 8, and parents educational attainment at child s age 0. The interaction term was not significant for kindergarten achievement (B = 3.026, p =.142), family risk status at child s age 8 (B =.209, p =.392), or parents educational attainment at child s age 0 (B =.03, p =.758). This suggests there was no selective attrition in the study sample. Effect Sizes To summarize, the preschool group had higher levels of educational attainment than the comparison group in terms of high school completion, highest grade completed, and college attendance (see Table 3). In relation to the effect sizes, it is 0.30 for high school completion, which indicates the effect size was between small and medium. It is 0.23 for highest grade completed, which indicates a relatively small effect. According to Cohen s (1988) general suggestions for interpreting the d index, these effect sizes do not seem large. However, effect sizes should be interpreted with caution because the social and economic significances of outcomes
15 EARLY INTERVENTION AND EDUCATIONAL ATTAINMENT 189 vary dramatically. Percent improvement over comparison group provides a different way to understand the differences between groups. For example, the CPC preschool group is 28.5% improvement over the comparison group in relation to college attendance, although the effect size is only 0.18, indicating an small effect. The alternative methods used to present the difference between groups may make the results more comprehensible to policymakers. In relation to subgroups, males benefited more from the preschool program than females on high school completion. DISCUSSION This study makes several unique contributions to the field of early intervention research. First, multiple measures of educational attainment from a large-scale federally funded program were examined. Most findings for educational attainment were from model programs with relatively small sample sizes. The sample size of this study was over 1,000. A larger sample size increases the statistical power of the results (Cohen, 1988). In addition, college attendance has only been examined in three programs, and this study investigated college attendance of CPC participants for the first time. Second was the finding of subgroup analysis. Gender was found to be significantly interacted with CPC program participation. Males benefited more from the CPC program for educational outcomes. Third, the findings are persistent from earlier CLS studies (Reynolds, 2000; Reynolds, Temple, Robertson, & Mann, 2002), which provide support to the lasting effect of the CPC Preschool program into early adulthood. Finally, group differences were robust across a wide range of analyses and models. Various sets of covariates were used to examine the group differences, and the findings were consistent. In addition, the group comparability of the sample and attrition analyses also increased the confidence that the findings reflected the program s influence rather than other demographic factors. Table 5 summarizes findings regarding high school completion from major longitudinal studies. Findings from the Perry Preschool program, CLS, and the CPC program are consistent. The program groups had higher rates of high school completion than the comparison groups by 10 percentage points or more. The Abecedarian Project differed from these studies in that the findings showed no significant group difference in rates of high school completion, but they found that participation in the early intervention program was positively associated with more years of education and a higher rate of 4-year college attendance. Gender subgroup analysis indicated that males benefited more from the CPC preschool program than females in relation to rates of high school completion. This finding is consistent with an early study from the CLS (Reynolds et al., 2001). However, it is different from those of other studies, which found females benefited
16 190 OU AND REYNOLDS TABLE 5 Rates of High School Completion by Studies a Program Age N Program Group % Comparison Group % Difference % Perry Preschool Program (Berrueta-Clement et al., 1984; Schweinhart et al., 1993) Abecedarian Project (Campbell et al., 2002) b Consortium for Longitudinal Study c (Royce et al., 1983) Child-Parent Center preschool program (Reynolds et al., 2001) ,281 1, a Rates for Perry Preschool Program and the Abecedarian Project were only available in two digits. b The rates for 4-year college attendance were 36% for the preschool group, and 14% for the comparison group (p <.01). c Only four projects out of those cited in Royce et al. (Beller, Gray, Karnes, and Weikart) had subjects old enough to investigate for high school completion, and the average age for subjects was 20. more from early intervention programs (Barnett et al., 1998; Beller, 1983; Campbell et al., 2002; Gray et al., 1983; Lally et al., 1988; Oden et al., 2000). The different context among the studies might be the reason for the inconsistent findings. The study sample is living in an inner city, which is very different from other study samples. Minority males are at higher risk than females in inner cities. College Attendance The findings support the positive relations between participation in CPC preschool and high school completion and highest grade completed. However, the finding regarding college attendance was weak; even though preschool participants had a higher rate of college attendance (23% vs. 17.9%, effect size, 0.18), the difference was not consistently significant. Nevertheless, this finding at age 22 is consistent with the finding from the Perry Preschool program for participants at age 27 (Schweinhart et al., 1993). They found a positive relation between program participation and high school graduation and highest grade completed, but not for postsecondary education (33% vs. 28%; effect size, 0.11). Potential reasons for the relatively small difference between groups in college attendance are explored here. The factors contributing to attendance in postsecondary education are complex. In particular, factors other than an individual s intention to attend college, such as family background and economic barriers, play important roles. Research has shown that socioeconomic factors, such as parents educational attainment, occupation, and family income, are related to college at-
17 EARLY INTERVENTION AND EDUCATIONAL ATTAINMENT 191 tendance (McMurrer & Sawhill, 1998; U.S. Department of Education, 2003). For example, in 2001, for youths who completed high school and whose parents were not high school graduates, only 39% enrolled in college the October after completing high school. This is much lower than the 81.3% of those youths whose parents education was bachelor s degree or higher (U.S. Department of Education, 2003). Family circumstances, such as youths need to help out at home or work full-time to support their families, might prevent or delay them from attending college. This is more likely to be relevant for youths who come from low-income families. In 2001, 43.8% of high school completers from low-income families (bottom 20% of all family incomes) enrolled in college the October after completing high school compared to 56.5% from middle-income families (60% of all family incomes between the top 20% and bottom 20% of all family incomes), and 79.8% from high-income families (top 20% of all family incomes; U.S. Department of Education, 2003). Economic barriers, such as availability of financial aid and the cost of college, make it harder for poor or minority youth to pursue postsecondary education, even if they intend to enroll in college or qualify for attending college (Heckman, 2000; McMurrer & Sawhill, 1998). If schools can provide more opportunities for financial aid, such as scholarships, fellowships, part-time jobs, or student loans, this assistance might help youths overcome the economic barriers that prevent them from attending college. Other than those potential reasons regarding the small differences between the preschool and comparison groups in college attendance, later measures of college attendance will account for possible delayed effect of enrollment because delayed college entrance is prevalent in low-income minority groups. Although group differences in college attendance are not consistent in terms of statistical significance, the preschool group had a 28.5% improvement over the comparison group in college attendance. Not only are the economic returns to a college education such as lifetime earnings substantial, but the nonmonetary benefits to a college education such as health are also important (Day & Newburger, 2002; Pascarella & Terenzini, 1991). High school completion has become a basic requirement for economic success, but a college education has emerged as the strongest predictor of socioeconomic status success (McMurrer & Sawhill, 1998). The association between CPC preschool participation and college attendance should continue to be examined in future studies. Limitations There are three limitations of this study. First, the study used a quasi-experimental design, and thus the confidence in the inference about program effects may not be as strong as in a randomized experiment. Nevertheless, because the study used a quasi-experimental design, some additional analyses were conducted to
18 192 OU AND REYNOLDS strengthen the validity of findings. For instance, comparisons between the preschool group and the comparison group were conducted regarding background variables to see if the two groups were similar before they participated in the program. The findings indicate that there was no difference between the two groups. Similar findings were also reported in earlier studies from the CLS (Reynolds, 2000). It should be noted that it is likely that the differences resulting from CPC preschool participation have been underestimated in the study, because the comparison group received an alternative intervention rather than no intervention. In the mid-1980s, full-day kindergarten programs were more than the usual educational treatment. In addition, attrition analysis was conducted to investigate whether there was selective attrition in the study sample. Heckman s (1979) selection model was used to examine the selective attrition. The findings indicate that the attrition was not systematic, which provides support for the hypothesized similarity between the study sample and the original sample, and thus increases confidence regarding group comparability. With attrition taken into account, the difference between groups was 11.9 percentage points, and the effect size of preschool participation for high school completion was 0.31, which increased slightly compared to effect sizes after controlling for different sets of covariates, but not taking attrition into account. A second limitation was generalizability. Although the study supports findings from other early intervention programs conducted in other locations, the results should not be broadly generalized to other populations or other contexts. Because the majority of the study sample was comprised of African Americans living in an inner city, the results might be generalized to this population under the same context. Finally, the measure for college attendance was a preliminary one, and attendance at either 2-year or 4-year colleges was counted. Although administrative data were obtained from colleges in Chicago area, it is likely that some participants were missed from the record search due to various reasons, such as students having moved to other states. The rate of college attendance of the study sample might be underestimated. Implications Results indicate that an established federally funded early intervention program is linked to higher educational attainment for economically disadvantaged children, which has implications for social policy on investment in effective early interventions. The nation has made investments to help disadvantaged children get ready for school by expanding early intervention programs like Head Start. The findings demonstrate that school-based publicly funded programs can have effects into adulthood. Prevention and cost-efficient investments have become higher priorities in funding social programs. The timing of early childhood education programs
19 EARLY INTERVENTION AND EDUCATIONAL ATTAINMENT 193 makes them more cost-efficient and effective than intervention programs conducted later in life (Heckman, 2000), such as school dropout prevention programs. Higher educational attainment is an important factor for social mobility, and in particular for urban, poor, and minority youths, because the change of occupation and stratum might improve later life chances (Day & Newburger, 2002; McMurrer & Sawhill, 1998). Therefore, educational attainment is a good predictor of economic well-being and earnings. For example, the average annual income of dropouts ages 25 to 34 was 30% less than the income of high school completers in 2000 (U.S. Department of Education, 2002), and dropouts headed half the welfare families and accounted for half of the prison population in 1992 (Educational Testing Service, 1995). Higher educational attainment will improve individuals future well-being. Consequently, the lasting effects of early intervention programs on educational attainment can benefit not only the participants but also society, with factors such as higher projected lifetime earnings, less juvenile delinquency, or less adult crime (Barnett, 1995; Heckman, 2000; Karoly, 2000; Karoly, Kilburn, Bigelow, Caulkins, & Cannon, 2001; Masse & Barnett, 2002; Reynolds et al., 2002; Weber, Foster, & Weikart, 1978). For instance, Reynolds et al., (2002) found that the CPC preschool program provided a return to society of $7.14 per dollar invested by increasing economic well-being and tax revenues, and by reducing public expenditures for remedial education, criminal justice treatment, and crime victims. In conclusion, high-quality effective early intervention should be promoted. Adding to a now critical mass of studies showing positive long-term effects into adulthood (Barnett, 1995; Campbell et al., 2002; Garces et al., 2002; Karoly et al., 1998; Reynolds, 2000; Schweinhart et al., 1993), findings from the CPCs support the effects of high-quality preschool experiences before children enter kindergarten. ACKNOWLEDGMENTS Preparation of this article was supported by the National Institute of Child Health and Human Development (R01HD034294). REFERENCES Aldrich, J. H., & Nelson, F. D. (1984). Linear probability, logit, and probit models. Beverly Hills, CA: Sage. Barnett, W. S. (1995). Long-term effects of early childhood programs on cognitive and school outcomes. The Future of Children, 5(3), Barnett, W. S., Young, J. W., & Schweinhart, L. J. (1998). How preschool education influences long-term cognitive development and school success: A causal model. In W. S. Barnett & S. S.
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