AHigh-SchoolPrograminComputer JudithGal-EzerCatrielBeeriyDavidHarelz AmiramYehudaix Science

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1 AHigh-SchoolPrograminComputer JudithGal-EzerCatrielBeeriyDavidHarelz AmiramYehudaix Science high-schoolcurriculumincomputerscienceandsupervisingthepreparationofacomprehensivestudyprogrambasedonit.thenewprogramemphasizesthefoundationsofalgorithmicthinking,andteaches programmingasawaytogetthecomputertocarryoutanalgorithm. Thepaperdiscussestheprogramanditsinitialimplementation. Theauthorsarepartofacommitteethathasbeendesigninganew Abstract tury,havingdramaticallyandirrevocablychangedthewaywelive,and 1Introduction Computersarewithoutdoubtthemostimportantinventionofthe20thcen- mostlyforthebetter.oneoftheuniversallyagreeduponimplicationsof Keywords:computerscience,curriculum,education,high-school. yearspentatthescienceteachingdept.,theweizmanninstituteofscience,rehovot, Israel.) atcornelluniversity,ithaca,ny,andwaspartiallysupportedbygrantsaf#f Science,Rehovot,Israel.(Partofthisauthor'sworkwascarriedoutduringasabbatical TheOpenUniversityofIsrael.(Partofthisworkwascarriedoutduringasabbatical (tok.birman).) (toF.Schneider),NSF#CCR (toB.Bloom),andNSF#CDA ydept.ofcomputerscience,thehebrewuniversity,jerusalem,israel. zdept.ofappliedmathematicsandcomputersciencetheweizmanninstituteof xdept.ofcomputerscience,tel-avivuniversity,ramat-aviv,israel 1

2 (CS),predatestheinventionofcomputers.Therstdecadesofthetwentiethcenturysawacrystalizationoffundamentalconceptsinthisdiscipline, mathematiciansandphilosophers.morerecently,fueledinpartbytheinventionofcomputersandtheirwidespreaduse,thestudyofcomputinghas accompaniedbydiscoveriesonthelimitationsofcomputationthatsurprised However,computingasascienticdiscipline,nowcalledcomputerscience atestheneedforintroducingcomputersintohigh-schoolcurricula. thisisthateducatedpeopleshouldbecomputer-literate.this,inturn,cre- bloomed,andcsisnowrecognizedasanautonomousscienticdiscipline.its andimplementationofcomputingsystems.itsconceptsareinuencingwork scopeincludesthestudyandanalysisofalgorithmicprocesses,theirpower andlimitations(sometimescalledalgorithmics[k,h]),aswellasthedesign computer-literacyortheuseofcomputersasateachingaidinotherdisciplines.whencomputinghasbeentaughtinhigh-schoolasanautonomoutralnotionsandthoughtstylesarebecomingwidelyassimilated.clearly,a inotherscienticdisciplines,and,asinotherscienticrevolutions,itscen- modernhigh-schoolcurriculumshouldreectthisgrowingimportance. onesideofthecoin.ourinterestisfarmorefoundational,andaddresses subject,theemphasishasbeenmostoftenonthetechnicalitiesofaprogramminglanguage;atbest,studentslearnedto\code".however,codingisonly theneedtoestablishcsasanacceptedscienticsubjectonthehigh-school Mosthigh-schoolactivityincomputinghascenteredaroundcoursesin physicsandchemistry. levelofeducation,tobetaughtonaparwithothersciences,suchasbiology, changesfarmorerapidlythanthebasicideasofthescienceofcomputing, coreofthesubjectislongevity.toalargeextent,computertechnology whichcenteronthenotionofanalgorithmanditsuseincomputingsystems. Thisscienticfacet,atleastfromtheexperienceofthe60yearsorsosince thepioneeringdaysofcs,haslastingandfundamentalvalue.thus,even thoughaproposedhigh-schoolprogramshouldenhanceastudent'sability Asinanyscienticsubject,oneofthecriteriaforwhatconstitutesthe toexploitcomputersbenecially,itsbackbonemustbebasedonthescience. exposedtocs,agoodcurriculummustalsoaimatbreadthandversatility. thehigh-schoolyearsaretheonlyperiodinwhichmanystudentswillbe independentofspeciccomputersandprogramminglanguages.also,since Muchoftheinsight,knowledgeandskillsitprovidesshouldbeofvaluethatis Thispaperdescribesanewhigh-schoolcurriculumincomputerscience, 2

3 thathasbeenproposedbyacommitteeformedin1990bytheisraelministry ofeducation.itsemphasisisonthebasicsofalgorithmics,anditteaches programmingasawaytogetacomputertocarryoutanalgorithm. curriculumitself,withitsgoalsandprinciplesspelledoutinsomedetail, andsection4discussesourexperienceinimplementingtheideas.section5 summarizessometopicsforfurtherwork. 2Background Section2providessomebackgroundforourwork,Section3presentsthe onsuchissuesas:whatreallyiscs?whatisitsrelationshipwithother earthskills.therehavealwaysbeenlengthy,oftentedious,controversies isnotonlythetenderageofoureldthatcausesproblemsfortheeducator. Thenatureoftheelditselfisafactortoo.Ontheonehand,CSresembles mathematics,withitsformalmethodsandabstractthinking,butontheother handitisverymuchanengineeringdiscipline,requiringconcrete,down-to- CSisarelativelyyoungdiscipline,andCSeducationisevenyounger.Butit educatedcomputerscientist?somerelevantreferencesonthesequestions elds?howdoitssubeldsrelatetoeachother?whatcharacterizesawellels,andwehavementionedsomeofthisworkinasidebar.particularly are[d,k,p,b]. notableisthehigh-schoolcurriculumdesignedbyacm'sspecialtaskforce basicphilosophy,thegoalsandscopeofthetwoprograms,andtheextent [M+].OurworkwasindependentoftheACMeort,anddespiteasimilar toaone-year,120-hourcs-orientationcourse,whereasourscanreach450 ofthecommittees'mandate,arequitedierent:acm'sprogramamounts TherehasbeenconsiderableactivitysurroundingCScurriculaonalllev- responsibleforeducationalpolicyanditsimplementation,wearealsoheavilyinvolvedinsupervisingthemanyadditionalactivitiesrequiredtoturna skeletoncurriculumintoawidely-usedworkingprogram.thisincludesthe OurprogramwasdesignedtotIsrael'sparticulareducationalneeds,but hours,taughtoverthreeyears,andisreallyanextensivehigh-school-level studyofthesubject.moreover,havingbeenappointedbythebodydirectly appearstobeapplicablemorewidely.tohelpgetafeelingforthecontext preparationofdetailedcourseware,thedesignofteachers'trainingcourses, thedelicatetaskoffollowinganinitialeldtest,andsoon. 3

4 ofourwork,wehaveprovidedabriefdescriptionoftheisraelieducational systeminasidebar. riculumeversincethemid-1970s,butithasyettobecomeafullyaccepted scienticsubjectlikephysics,biologyorchemistry.insteadoftheusual3- unitand5-unitprogramsstudiedtowardsthematriculationexams(seethe Partlyasaresultofthis,theuniversitiesinIsraelhavenevertakenCSin sidebar),cswastaughtin2-unitand4-unitprograms.moreover,many high-schoolssimplydidn'toercsatall,oroeredthe2-unitprogramonly. ComputersciencehasexistedasasubjectinIsrael'shigh-schoolcur- 1970swasbasedonasolidanddetailedcoursefocusedonprogrammingin intheothersciences. universitycandidate,high-schoolunitsincsarenotworthasmuchasunits high-schoolasseriouslyastheothersciences.intheoverallevaluationofa educationalissues.however,courseware(studybooks,teacher'sguides,etc.) BASIC.Inaddition,itcalledforaratherextensivesetofelectiveportions.If toreectchangesintheeldandabetterunderstandingoftherelevant theproblemsomewhat,andbynowwemighthaveonlyhadtoupdateit thiscurriculumweretohavebeenimplementedinfull,itcouldhavealleviated ThecurriculumdevelopedbyaMinistryofEducationcommitteeinthe totheentireplannedcurriculumthatcommitteedidhavealgorithmsin besideslearningtoprograminbasic,thestudentswerenotalwaysexposed mind,buttheemphasisinpracticewasonteachingandexercisingtheuse werenotalwaysavailablefortheelectivesinthe1970sprogram.sothat isvisiblefromthestart.whiletherearewell-denedrequirementsforqualifyingteachersinmostotherhigh-schoolsubjects,thesituationincsisquite taughtthematerialastheysawt. werelessthanadequatelyknowledgeableaboutthesubjectmatter,andoften ofaprogramminglanguage.inaddition,someoftheteachersthemselves maticsprograminthehandsofaself-taughtinstructor,oronewithonly dierent.noself-respectingschoolsystemwillleaveitsphysicsormathe- high-schooleducation.yetthisisexactlywhatveryoftenhappensincs programsinmanycountries.itwasonlyin1992thattheusaorganization Indeed,the\teacherissue",aswecallit,isaveryproblematicone,and NCATE(NationalCouncilforAccreditationforTeacherEducation)adopted standardsforteacherpreparationprograms,totakeeectstartingin1994 [TTK]. GettingbacktothedevelopmentofcurriculainIsrael,variousnewunits 4

5 computerscience. curriculum,whichsometimesentailedmovingevenfurtherawayfromtrue intheeducationalaspectsofmathematicsandcomputerscience(therstlistedauthorofthispaper),threecomputerscientistswhoareinvolvedin computerliteracy).someschoolsadoptedtheseinplaceofpartsorallofthe the1980s(amongotherthingstomeetthegrowingdemandforteaching basedonlogoandanelectronicspreadsheetlanguageweredevelopedin educationalissuesonvariouslevels(theremainingco-authorsofthispaper), twoexperiencedhigh-schoolteachersofcomputerscience,threeeducation andcomputersciencesection,andtheheadofthatsectionhimself. professionalsfromtheministryofeducation,twoofthemfromthecomputer Ourcommitteewasformedin1990.Itconsistsofaresearcherspecializing thewholeissuemustbere-addressed,andanewandcarefullythought-out computerscienceprogrammustbedevelopedforhigh-school(i.e.,grades10 through12).wewereconvincedthatthecommitteeshouldnotonlydecide onthegeneraltopicsandprinciples,butshouldalsopreparedetailedandrigoroussyllabiforallunitsintheprogram;itshouldhelpformandsupervise theteamswhopreparethecourseware,providingthemwithcontinuoustechnicalfeedback;itshouldbeinvolvedinthedevelopmentofteachertraining ofitsrecommendations. 3TheNewProgram 3.1Underlyingprinciples Beforegettingintoamoredetaileddescriptionofthenewprogram,itis helpfultopinpointtheprincipleswehaveusedtoguideourwork,someof exposedtoanycomputersciencebeforeembarkingonit.thisisoneofthe inmindthattheprogrammustintroduceanewsubject;studentsarenot whichrecapitulateissuesdiscussedabove.inreadingthem,ithelpstokeep maindierencesbetweencomputerscienceandotherhigh-schoolsubjects. Computerscienceisafull-edgedscienticsubject.Itshouldbetaught inhigh-schoolonaparwithotherscienticsubjects. Westartedoutbyreviewingtheexistingsituation,andconcludedthat activities;anditshouldguideandfollowasmall-scaleinitialimplementation 5

6 Theprogramshouldconcentrateonthekeyconceptsandfoundations Twodierentprogramsareneeded,onefor3unitsandonefor5.The oftheeld.themainnotiontobeemphasizedthroughouttheprogramisthatofanalgorithmicproblem,andanalgorithmasasolution thereof.tosomeextent,themoregeneralnotionofasystem,andthe accompanyingprinciplesofmodularizationandabstractionshouldalso bediscussed.othertopicsaretobeviewedasbuildinguponthese. rstisforstudentswithonlyageneralinterestincs,andthesecond, Eachofthetwoprogramsshouldhaverequiredunitsandelectives. tocomputerscience,sothatsomeattemptatcomprehensivecoverage shouldbemade. intoaccountthatformanystudentsthismightbetheonlyexposure whichshouldbedeeperandbroader,isforthosewithmorespecic interestincs.however,thedesignofthe3-unitprogramshouldtake Conceptualandexperimentalissuesshouldbeinterwoventhroughout ics,someofthesearelesscrucialthanothersandcanbemadeelective. Moreover,varianceandexibilityisimportantforitsownsake. Whiletheentireprogramshouldconsistofcentralandimportanttop- Twoquitedierentprogrammingparadigmsshouldideallybetaught.It thelaboratory.thistwotrackapproach,whichwedubbedthe\zipper Itreferstosubjectsthataretaughtintheclassroom,ratherthanin oninasidebar. theprogram.theword`conceptual'heredoesnotmean`impractical'. principle",isoneofthesalientpointsofourprogram,andiselaborated Awell-equippedandwell-maintainedcomputerlaboratoryismanda- ishighlyrecommendedthatastudentshouldlearna\mothertongue" rst,butthen,onamorehumblescale,beintroducedtoanotherlanguage,ofradicallydierentnature,thatsuggestsalternativewaysotory.thisistheresponsibilityoftheschoolsystem,andentailssettingthingsuptosupportlaboratorysessionsandadequateindividual algorithmicthinking.thisemphasizesthefactthatalgorithmicsisthe centralsubjectofstudy. \screen-time"forstudents.6

7 TeacherscertiedtoteachthesubjectmusthaveadequateformalCSeducation.Anundergraduatedegreeincomputerscienceisamandatory scientistsonboard,aswellascshigh-schoolteachersandresearchers Newcoursematerialmustbewrittenforallpartsoftheprogram.The incomputerscienceeducation. teamsthataretopreparethecoursewaremusthave\real"computer TheprogramshouldfocusonthemostbasicandlastingconceptsofCS.It requirement,asisformalteachertraining. 3.2StructureandContents trainthestudentstodealwithintellectuallydemandingtasks. butwillalsorelatethemtothepracticalsideofcomputing,anditshould Theprogramcomesintwoversions,a3-unitoneanda5-unitone.The mustbechallenging,inthesensethatitwillnotonlyteachthefoundations, below,fromthefollowinglistofmodules: isdeterminedbytheschools.)theprogramsareconstructed,asexplained thepaperareabsolute.thewaytheyarespreadoutoverdaysandweeks formerconsistsof270hoursofstudy,andthelatterof450.(allhoursin 1.Fundamentals1and2(2units;180hours):Thismodulepairpro- 2.Advancedprogramming(1unit;90hours):Thismoduleisreally ducesmostoftheaforementionedcentralconcepts,andinaparallel videsthefoundationfortheentireprogram.itistheonethatintro- minglanguage. realizationtrackteacheshowtoapplytheminaproceduralprogram- 3.Secondparadigm(1unit;90hours):Thismoduleintroducesthestudenttoasecondprogrammingparadigm,whichisconceptuallyquittems. dierentfromtheproceduralapproachadoptedinmodules1and2. acontinuationoffundamentals.itconcentratesondatastructures, introducingabstractdata-typesintheprocess,andalsotakesastep beyondstand-alonealgorithms,todiscussthedesignofcompletesys- 7

8 4.Applications(1unit;90hours):Thismoduleconcentratesonone Currentlyapprovedarelogicprogrammingandsystem-levelprogrammingunits;otherpossibilitiesincludeobject-orientedprogramming, 5.Theory(1unit;90hours):Thismoduleisintendedtoexposethe functionalprogramming,andconcurrentprogramming. approvedaretwoalternatives:afullunitonmodelsofcomputation studenttoselectedtopicsintheoreticalcomputerscience.currently particularkindofapplication,teachingbothprinciplesandpractice. Currentlyapprovedalternativesarecomputergraphicsandmanagementinformationsystemsputationandnumericalanalysis. (mainlyautomata),andatwo-partunitconsistingofmodelsofcom- paradigm,theoryandapplications.sincesecondparadigmandapplications canbetakenonthe3-unitleveltoo,weenvisionsomewhatdeeperversions thethirdunitinthe3-unitprogramthereisachoicebetweenthesecond ofthembeingdevelopedforthe5-unitprograminthefuture. paradigmandapplications.inthe5-unitprogram,advancedprogrammingis mandatory,andthefourthandfthunitsarechosenfromamongthesecond ThetwoFundamentalsunitsaremandatoryforbothprograms.For 3.3Themodules Wenowdescribethecontentsofthemodules: Fundamentals1 willnotstudyanymorecomputerscience.itcoversthebasicconceptsofan Itisalsointendedtobeusableasastandalonemini-courseforstudentswho algorithmicproblemanditssolution thealgorithm.italsodiscussesfunctionsasarenementmechanism,andintroducesthenotionsofalgorithmic correctnessandeciency.thecontentsofthismoduleisdescribedinmore detailinaspecialsidebar. Thisisthebasisoftheentireprogram,andistaughtinthe10thgrade. approachtakeninthisandothermodules.basically,eachsubjectisintro- Thesidebaronthezipperprincipleexplainstheunderlyingpedagogical 8

9 rstcourse,notablyfunctionallanguagessuchasscheme[as].sincethis recastinpractical,implementationalformusingaprogramminglanguage. guage the\mothertongue";seee.g.,[w,ba,lp].manygoodarguments havebeenmadeforadoptingnon-proceduralstylesofprogramminginthe ducedrstonaconceptuallevel,includingmanualexercising,andisthen webecameconvincedthatforhigh-schoolitisprobablybesttoremainin themainstream,andadoptaprocedural(imperative)styleofprogramming. isstillcontroversial,andthereisnoclearagreed-uponapproachemerging, Muchhasbeensaidaboutthesignicanceoftherstprogramminglan- languageissueanyfurther. programitselfdoesnotimposeaspeciclanguage,andthefuturemight thecurriculumisactuallylanguageindependent,weshallnotdwellonthe ndteamsdevelopingcoursewarethatusesotherlanguages.sincemuchof wesupportdevelopmentofapascalversionofthematerial.however,the Wethusdecidedtoadopta\vanilla"proceduralapproach,and,asofnow, ofnewfacetsofalgorithmicanalysisanddesignareemphasized,suchas rstrevisitsandexpandsuponsomeofthetopicscoveredinthe10thgrade, inordertodeepenthestudent'sunderstandingofthatmaterial.anumber Fundamentals2 two-dimensionalarrays.timeeciencyistreatedinmoredetail,anda followingtopicsaretaught:recursion(onlyfor5-unit-ers),procedures,and stepwiserenement,top-downandbottom-uptechniques.inaddition,the Thissecondpartofthebasicmaterialistaughtinthe11thgrade.It sorting. Advancedprogramming specialsectionisdevotedtomoreadvancedproblems,suchassearchingand followsintroductorycomputerscienceisusuallydevotedtodatastructures anddatatypes.wehadmoregeneralgoalsinmind,namelytoendowthe mainstructuringtool,hereabstractdatatypesareaddedtohelpinhandling studentwithabasicunderstandingoflargersystemsandtheirorganization principles.newdatastructuresaretaught,suchasstacksandbinarytrees. WhereasintheFundamentalsmoduleproceduresandfunctionswerethe ThisisacontinuationofFundamentals.Inuniversities,thecoursethat alsoinvolvestheimplementationofoneortwosmallsystems. largersystems.dynamicmemoryallocationistouchedupon,andthemodule 9

10 Secondparadigm factsandclausalrules.programmingiscarriedoutinprolog,withrecursion, listsandtreestakingaprominentplaceinthematerial.thesecondpresents modulebasedonassemblylanguageisinpreparation.therstoftheseintroducesbasicnotionsfromlogic,anddiscussesknowledgerepresentationby theconceptualstructureofacomputersystem,andprovidesanintroductiontoprogramminginassemblylanguage.wewouldverymuchliketosee Currently,thereisalogicprogrammingmoduleavailable,andanother onfunctionalorobject-orientedprogramming,oraunitdevelopedaround additionalalternativemodulesdevelopedforthisunit,suchasonesbased relevantnon-csspecializationsinthistrackarethosethatrevolvearound concurrency. pectsofcomputation(forexample,inarchitecturaldesign).accordingly,two informationsystems(forexample,inhoteladministration),orgraphicalas- theminapplyingcomputerstotheprofessiontheyarepursuing.themost tocatertostudentsinthespecialtechnologicaltrack.1theunitshouldhelp Applications modulesarebeingdeveloped.oneisanintroductiontomanagementinformationsystems,whichdiscusseslogicalleanddataorganization,asystem's lifecycle,andbasicsystemsmodelingandanalysis.theotherisanintro- Indecidinguponthecontentsofthisunit,weweremotivatedbytheneed Theory ductiontocomputergraphics,whichdealswiththebasicsofrepresenting wewouldliketoseeadditionalalternativemodulesdevelopedinthefuture. databasesystemoracadpackage,andanalprojectisrequired.heretoo, andmanipulatinggraphicobjects,andtheiruseinproblemsolving.inboth Twomodulesarecurrentlyunderdevelopment,oneinmodelsofcomputationandtheotherinnumericalanalysis.Therstintroducesniteautomata, pushdownautomataandturingmachines,andelaboratesontheirrelative limitationsofcomputers.thesecondmoduleconcentratesontwomain power.italsopresentsthechurch-turingthesis,andbrieydiscussesthe 1However,theunitcanbetakenbyallstudents. Thisunitexposesthestudenttotopicsintheoreticalcomputerscience. modulesthestudentgetstouseaready-madesoftwarepackage,suchasa 10

11 equations.issuestreatedincluderound-oerrors,absoluteandrelativeerrors,approximatesolutionswitherrorcontrol,andill-conditionedproblems. topics:iterationsforrootextraction,andthesolutionoflinearsystemsof Twoversionsofmodelsofcomputationarebeingdeveloped,oneof90hours, whichcoversthefullunit,andtheotheranabridgedversionof45hours, 4.1Developingthematerial whichistakentogetherwiththe45-hournumericalanalysismodule. byappointingprofessionalteamstopreparedetailedsyllabi,tobefollowed, Whenwehadtherstversionofthecurriculumplannedout,weproceeded afterthecommittee'sapproval,bythedevelopmentofcoursematerial.2 4GettingtheProgramUnderWay possiblewouldtakepartintheeort.thishelpsensurethattheprogram withexperienceincseducation,andonehigh-schoolteacherofcs.wetried todistributethechoiceofteams,sothatasmanyacademicinstitutionsas isversatile,inthesensethatdierentscienticanddidacticapproachesare ofanisraeliuniversity,andhasthreetofourmembers.weinsistedthat therebeatleastonecomputerscientistonboard,oneacademicresearcher Atypicaldevelopmentteamcomesfromascienceteachingdepartment level,wherewecoulddrawuponaccumulatedexperience.indeed,several versionsofthesyllabiwereoftenneededbeforethecommitteewasabletogive process,despitethefactthatmanyofthetopicsaretaughtattheuniversity itsnalapproval.inaddition,thesyllabiwereoftenfurtherchangedduring represented. thepreparationofsyllabiturnedouttobestraightforwardincomparison theperiodofcoursewarepreparation,andevenduringtheeldtest.still, Preparationofthesyllabiforthevariousmoduleswasquitealengthy withthepreparationofthecoursewareitself. preparationofsyllabiandcourseware,andalsoinsomeaspectsoftheimplementation. becamemoreacuteinwritingthecourseware,wasthatofstudentpopulation. and5-unitprograms,reectingthesignicantdierenceinrequiredbreadth Ideally,wewouldhavepreferredtodevelopseparatecoursewareforthe3-unit 2Themembersofthecommitteewere,andstillare,deeplyinvolvedinallaspectsofthe Oneoftherstdicultieswefacedindevelopingtheprogram,which 11

12 alternativesinanysubjectuntiljustbeforethe11thgrade.infact,inthe encouragethis,asstudentsarenotrequiredtomakedecisionsonprogram 10thgrade,whenourprogramstarts,manystudentshavenotyetdecided anddepth.inreality,thewaytheschoolsaresetupinisraeldoesnot whethertheywillbetakingcomputerscienceformatriculationatall.in the10thgrade,atypicalscience-orientedstudygroupstudiesallthemain collectionofstudents,includingfuture5-unit-ersaswellasoneswhoarenot tevenforthe3-unitprogram. scienticsubjectsavailableinhighschool,i.e.,physics,chemistry,biology, thingssuchthatpartofthematerialwouldbeaccessibletoaheterogeneous andinsomecasescomputerscience.studentsmaketheiractualchoiceof matriculationsubjectsonlytowardsthe11thgrade.hence,wehadtoplan elementary,butalsoofstand-alonenature.bythiswemeanthatthose weeklyhours,givingatotalof90hoursfortheyear,wehadtomakethe studentswhowillendupchoosingnottocontinuecsbeyondthe10thgrade, ofthesubject.thedescriptionoffundamentals1inthesidebarreectsthis. rst90hoursofstudy,i.e.,thefundamentals1module,notonlysuciently willhavebeengivenawell-rounded,ifsimple,viewoftheimportantaspects Sincecomputersciencestudiesinthe10thgradeusuallyinvolvethree Ontheotherhand,weshouldhaveknownthatprojectslikethisalwaystake ownrathersevereunderestimationoftheeort.ontheonehand,asacolschoolanduniversityteachingandinwritingcstextbooksandcourseware. longer,andaremorepainfulandtedious,thanoneplans.anyway,wedecidedtostartthedevelopmentofacoreprogram,consistingofthemandatorlectionofindividuals,ourcommitteehasextensiveexperiencebothinhigh- Anotherproblematicaspectofthedevelopmentofcoursewarewasour justied,amongotherreasonsbecauseouroptimismwasgreatlyexaggerated. availabilityofgoodcorematerialwouldhelptheprogrambeadoptedbythe modulesbutonlyasmallnumberoftheelectives.ourrationalewasthatthe Now,fouryearslater,westilldonothavenalversionsofcoursematerial foreventhecoreprogram.hadwetriedtoshootforamaximalprogram MinistryofEducationociallyastheCSprograminhigh-school,andput fromthestart,thesituationmighthavebeenevenworse.thegoodnewsis intooperationinmanyschools.then,wereasoned,therewouldbesucient thatatpresentwehavesatisfactorysyllabiformostoftheaforementioned supporttodrivethedevelopmentofadditionalmodulesasneeded. Inretrospect,thedecisiontodeveloponlyacoreprogramrstwasfully 12

13 modules,andcoursewareforseveralofthemthatiseithersatisfactoryoris materialisthoroughlyclass-tested,andalsopossiblyrewritten. stillneeded,ofcourse,sincewecannotclaimtohavenalversionsuntilthe atleastgoodenoughtogetusthroughtheinitialperiod.improvementsare budgets.thewaythingsaresetupinisrael,committeessuchasoursdonot haveoperatingbudgets,andcanonlymakerecommendationstotheministry toalargeextentonourcontinuousabilitytoconvincetheministrypeople ofeducation.thismeansthatthesuccessoftheproposedprogramdepends thatitisworththeirinvestment. Coursewarepreparationonsuchalargescaleclearlyrequiressignicant cultyofconvincingschoolstoparticipateinanewandembryonicprogram, 4.2Teachingthematerial butalsothatofndinggoodteachers. IntheFallof1991westartedaverylimitedeldtestforpartsofthenew maindicultiesinimplementingtheprogram.theanomalyisthatmost program.itrstinvolved8studygroupsin5schools,andby1994ithas unacceptable,andoneofthecommittee'sdecisionshasbeentorequiresuch growntoaround40groupsin9schools.thesesmallnumbersreectthedif- B.Ed.inCSeducation. adegreefromanyteacherseekingapermittoteachcsinhigh-school.3 CSteachersdonothaveauniversitydegreeincomputerscience.Thisis Specically,werequireaB.Sc.oritsequivalentinCS,oranappropriate Asmentionedabove,theteacherproblemturnsouttobeoneofthe teachingprogrammingandcsinhigh-schoolsforyearswithoutsuchformal ourpresentproblems.thereisalargegroupofteacherswhohavebeen gradualimprovementintheoverallqualityofcsteaching,itdoesnotsolve operational,butthemajoritywillprobablywanttocontinue.fortheselatter training.someofthesemightquitwhenthenewprogrambecomesfully ones,wehaveoutlinedaspecialcrashcourse,consistingofaround6basic Whilewearecondentthat,iffollowed,thispolicywillbringabouta inthe11thand12thgradesofhigh-school.however,inviewofthejobmarketsituation, requiredtohaveaseconddegree(m.sc.oritsequivalent)toteachafullscienticprogram wehavetriedtobemorerealistic. 3TheMinistryofEducationocialregulations,rarelyadheredto,arethatateacheris 13

14 isfamiliarwithlogicprogrammingorinformationsystems,andeventhose subjectsthataretaughtincsdepartmentsintheuniversities.4teachers withoutcsdegreeswillberequiredtocompletethesecoursesinordertobe allowedtoteachthenewprogram. whoarecoulddowithhelpinthedidacticaspectsofteachingsuchtopics teachthemodulesofthenewprogram.forexample,noteverycsgraduate inhigh-school.thefewteacherschosenfortheeldtest,althoughbetter trainedthanothers,stillhadtospendconsiderabletimeandenergyinadhocteachertraining,usuallyprovidedbythedevelopersofthecourseware Inaddition,eventhebestofteacherswillneedsometraininginorderto inaccordancewiththecommittee'sguidelines.thiswasnecessary,inpart, emphasizedtraditionalowcharts,andtheyfelttheywerebeingdeprived teachersexpresseddisapprovalofchangesinemphasis.forexample,wede- todispelsomebeliefsandhabitsoftheparticipatingteachers:intheinitial phasesoftheeldtestmanyofthemfeltmorecondentteachingwhatthey ofanimportanttechnicaldevice;weemphasizedpseudo-codeinalgorithm knewwell,likethetechnicalitiesoftheprogramminglanguage.also,some thecommitteefacesinthefuture,andwillrequirelotsofattention. itseemscertainthatwithinacoupleofyearswewillhavetodevelopa design(asopposedtodirectcoding),andtheyfeltthisnewmediumwastoo vague. inthisinitialimplementation.oneistheincrediblydiversebackgroundsof getinvolvedinthenewprogram.thisisoneofthemostchallengingproblems massiveinstructionalprogramforthegeneralbodyofteacherswhowantto Besidestheteacherproblem,thereareotherdicultiesthathavesurfaced Althoughthead-hoctraininggreatlyhelpedtheinitialgroupofteachers, thestudents.ontheonehand,theprogrammustcatertostudentswith Ontheotherhand,manystudentshaveextensiveprogrammingexperience. nofamiliaritywithcomputersatall(exceptpossiblyforcomputergames). beingpartofadegreeprogram. taughthackers,andhavedevelopedhabitsthatareoftenaseverehindrance Whatmakestheproblemparticularlyacuteisthatmostoftheseareself- thenecessarylaboratorytime;thelabsarealsoinadequatelymaintained. totheorderlystudyofalgorithmics. 4InIsrael'sOpenUniversitythesesubjectscanbetakenforcreditwithoutnecessarily Someschoolsareshortofcomputersandcannotprovidestudentswith 14

15 yetgiveincomingstudentsthesamebonuspointsforhigh-schoolcomputer scienceastheydoforothersciences.untilthishappens,manypotential studentswillhesitatebeforeagreeingtochoosecomputerscience,resulting Thereisstillalongwaytogobeforeschoolstreattheircomputerlabswith thesamerespecttheyconferontheirphysicsandchemistrylabs. however,isthatsofarithasbeenquitesuccessful.judgingfromteachers' inatroublingcatch-22situation. AnotherobjectivedicultyisthefactthatIsraeliuniversitiesdonot reportsandtheresultsofstudentexams,itseemsthatthemaingoalsare beingmet.theschoolsthemselveshaveinitiatedathree-foldincreaseinthe numberofclassesjoiningtheeldtestsinceitsinception. Astotheeldtestitself,thejuryisnotinyet.Ourcurrentfeeling, 5Postscript Insummary,wearequitehappywiththewaytheprogramisdeveloping,althoughourinitialexpectationsweresomewhathigher.Wehopethatwithiteninafewyears,toreectexperiencegainedinwide-scaleapplication.In addition,wementionedtheneedtodeveloptwoversionsoffundamentals, notreadyyet,andwefeelthateventhepartsthatarewillhavetoberewritertheless,thereisstilllotsofworktodo.somepartsofthecoursewareare twoyearsitwillbeadoptedthroughouttheisraelihigh-schoolsystem.nev- specializedvariantsbeingdevelopedinthefuture,perhapsbasedondierentdidacticapproaches,todealwithheterogeneousgroupsofstudentsor andnewalternativesforthesecondparadigmandapplicationsmodules.we mustalsodeviseeectiveteachertrainingcourses. putersciencestudyinhigh-school.withthisinmind,weenvisionmore totakeadvantageofstate-of-the-arttechnology,suchasinteractivetv. withproject-orientedstudy.finally,westronglybelievethattheprogram shouldevolvetousespecializededucationalsoftware(e.g.,asin[be]),and Ourworkcanbeviewedasprovidingabasicno-frillsprogramforcom- 15

16 Acknowledgements:Theworkreporteduponherereectstheeortsof manypeople.firstandforemostarethemembersofthecommitteeitself, whichischairedbyamiramyehudai.besidesourselves,itincludesben- ZionBarta(whoheadsthecomputerandcomputersciencesectioninthe MinistryofEducation),RoniDayan,EphraimEngel,MeirKomar,David References [AS]Abelson,H.,andG.J.Sussman,StructureandInterpretationofComputerPrograms,MITPress,Cambridge,MA,1985. Levant,andDavidSela.Wealsooweagreatdebttothemembersofthe anddedicationpermeatetheentireeort. variousdevelopmentteams,toonumeroustolistindividually,whosework [Ba]Baranauskas,M.C.C.,\ObservationalStudiesaboutNovices'InteractioninaPrologEnvironmentBasedonTools",Proc.7thInt.PEG [BE]Barwise,J.andJ.Etchemendy,Turing'sWorld,CSLIPublication, [B]Biermann,A.W.,\ComputerSciencefortheMany",Computer27:2 Conf.,Edinburgh,pp.537{549,1993. [D]Dijkstra,E.W.,\OntheCrueltyofReallyTeachingComputingScience",Comm.Assoc.Comput.Mach.32(1989),1398{1414. Stanford,CA,1993. [H]Harel,D.,Algorithmics:TheSpiritofComputing,Addison-Wesley, (1994),62{73. [LP]Lee,A.andN.Pennington,\TheEectsofParadigmonCognitive [K]Knuth,D.E.,\ComputerScienceanditsRelationtoMathematics", ActivitiesinDesign",Int.J.Human-ComputerStudies40(1994), 577{601. Amer.Math.Monthly81(1974),323{ (2nded.,1992). [M+]Merrit,S.,etal.,ACMModelHighSchoolComputerScienceCurriculum,AssociationforComputingMachinery,NewYork,

17 [P]Parnas,D.L.,\EducationforComputerProfessionals",Computer [W]Wexelblat,R.I.,\TheConsequencesofOne'sFirstProgrammingLanguage",Software{PracticeandExperience14(1981),733{740. [TTK]Taylor,H.G.,L.G.ThomasandD.G.Kneze,\TheDevelopment TeacherPreparationPrograms",J.TechnologyandTeacherEducation 1(1993),319{333. andvalidationofncate-approvedstandardsforcomputerscience 23:1(1990),17{22. 17

18 startingwithcurriculum'68[acm],followedbysubsequentversions,suchas[t+]. Overthepastyears,therehasbeenasteadyevolutionofuniversity-levelcurricula, 1Sidebar{SomeotherCSprograms andours. veryrecently[m+].inthetext,wetouchuponthedierencesbetweenthiswork therehavebeeneortstoestablishhigh-schoolcurriculaincomputerscience,see inthisisacm'staskforce,whoserecommendedcurriculumhasbeenpublished Onthehigh-schoollevelthingshavebeenslower,dueinparttothefailurein issuesconcerningspecicsystems)andgeneralcomputerliteracy.overtheyears, distinguishingadequatelybetweencomputerscience,computingtechnology(i.e., References e.g.,[r+],aswellasrelevantteachers'trainingcourses[p+,mjh,ttk].notable [ACM]ACMCurriculumCommitteeonComputerScience,\Curriculum'68Rec- [MJH]Maddux,C.D.,L.JohnsonandS.Harlow,\TheStateoftheArtinCom- [M+]Merrit,S.,etal.,ACMModelHighSchoolComputerScienceCurriculum, ommendationsforacademicprogramsincomputerscience",comm.as- soc.comput.mach.11(1968),151{197. AssociationforComputingMachinery,NewYork,1994. [T+]Tucker,A.,etal.,\ComputingCurricula1991:ASummaryofthe [TTK]Taylor,H.G.,L.G.ThomasandD.G.Kneze,\TheDevelopmentand PreparationPrograms",J.TechnologyandTeacherEducation1(1993), 319{333. ValidationofNCATE-ApprovedStandardsforComputerScienceTeacher nologyandteachereducation1(1993),219{228. putereducation:issuesfordiscussionwithteachers-in-training",j.tech- [R+]Rogers,J.,etal.,\ComputerScienceforSecondarySchool:CourseContent",Comm.Assoc.Comput.Mach.28(1985),270{274. [P+]Poirot,J.,etal.,\ProposedCurriculumforProgramsLeadingtoTeacher ACM/IEEE-CSJointcurriculumTaskForceReport",Comm.Assoc.Comput.Mach.34(1991),69{84. CerticationinComputerScience",Comm.Assoc.Comput.Mach.28 (1985),275{

19 setseducationalpolicyonalllevels,andthenimplementsitwiththeaidofspecializedcommittees,workteamsandprofessionalsupervisors. TheIsraelieducationsystemisbasicallycentralized.TheMinistryofEducation 2Sidebar{Israel'seducationsystem examsarebasedonacoreofrequiredsubjects,andseveraladditionalelectives. inanextensivesetofmatriculationexams(called\bagrut"inhebrew),which, hoursaweekforayear,orapproximately90hours.togetthroughthematriculationhurdle,astudenthastosuccessfullypasstheexamsinatleastsixsubjects, Subjectsaretaughtin\studyunits",eachofwhichdenotestheequivalentofthree tionalhigh-schoolyears(grades10{12)areoptional.thesethreeyearsculminate elementaryschool(grades1{6),andmid-levelschool(grades7{9).threeaddi- amongotherthings,arecrucialforforadmissionintoisraeliuniversities.the Studentsgothroughnineyearsofmandatoryeducation,usuallydividedinto accumulatingaminimumtotalof20studyunits,thoughmoststudentstakemore. suchastalmudandgeography.thesciencesarealsoelective,andincludephysics, English,Biblestudies,mathematicsandhistory,andthereareseveralelectives, biologyandchemistry.insomeschoolsthereisalsoatechnologicaltrack,inwhich typicallyrequirestudyingthesubjectfor5weeklyhoursthroughoutthethree yearsofhighschool.therequiredcoursesarehebrew(languageandliterature), thematerialandtheconceptualdepthofthepresentation.a5-unitprogramwould whichfollow3-unitand5-unitprograms,thatdiersignicantlyinthequantityof Manyofthesubjectscanbestudiedonvariouslevels,themostcommonof specializinginitlateroninlife. Itappears,therefore,thatourworkcouldbeapplicabletoothercountriestoo. with althoughinsomeplacesnotasextensiveas thatoftheisraelisystem. studentsstudysometechnicalsubjectintensively,withthegoalofpreparingfor schoolstudiesinmostcountriescontainascienticcomponentthatiscomparable Obviously,notwoeducationalsystemsarequitethesame.Nevertheless,high- 19

20 combiningtoformauniedwhole. inadvancedprogramming.infact,thesethreemodules,takentogether,constitute the\zipperapproach" alittleofthis,followedbyalittleofthat,andsoon, Amajorprincipleinthedesignofourprogram,andacrucialguidelineforteaching it,concernstheinterweavingofconceptualandexperimentalissues.wecallthis 3Sidebar{Thezipperprinciple discussedintheclassroom.then,ifneeded,relevantpartsoftheprogramming andideasinpractical,implementationalforminarealprogramminglanguage. languageareintroduced,andthestudentgetstopracticetheminthecomputer atwo-trackeort,theoneconceptualandtheotherarecastingoftheconcepts laboratory.manualproblemsolvingiscarriedoutpriortotheimplementational This\zippering"ismostvisibleinthetwoFundamentalsmodules,aswellas segment,aparticularlyimportantmatter,aswewantthestudenttounderstand thattheconceptsaremorefundamentalthantheirspecicrealizationinaparticularlanguage.heorshewillbecomemoreacutelyawareofthislater,when exposedtoanadditionalprogrammingparadigm,butwewanttodrivetheidea Progressalongthetwotracksismadeinparallel.Eachnewconceptisrst homefromthestart. programminglanguage.evenso,wedonotspendtoomuchtimediscussingthe illustratedwithinformal,naturallanguagedescriptions(suchas\capitalizeall introduced.aspecicprogrammingconstruct(forrepetitionitisthewhileorfor wordsintheinputlist")beforeanyprogramminglanguagerenditionsofitare usingit.thus,wedonotteachthewhilestatementasanentityinitsownright, but,rather,asoneofmanypossibleformsarepetitiveconstructcantakeonina statement)isthenpresented,andthestudentsapplyandpracticetheirknowledge Forexample,werecommendthatthenotionofrepetitioninalgorithmsbe understandtheabstract. whichtakesplaceintheschool'scomputerlaboratory. abstractnotion,sincemosthighschoolstudentsneedtheconcreteinordertofully Thezipperprincipleisreectedinthenalmatriculationexamtoo,partof 20

21 4Sidebar-TheFundamentals1module basisofboththe3-unitand5-unitprograms,itisalsointendedasastand-alone TheFundamentals1moduleistaughtinthe10thgrade.Besidesconstitutingthe Inactuality,mostofthemarereally\walltowall"topics,andaccompanythe experimentation(seesection4),andmightstillundergosomeminorchanges. atall. mini-courseforthosestudentswhochoosenottocontinuewithcomputerscience materialoftheentiremodule(aswellasthatoffundamentals2andadvanced recommendedhours,toshowwhenandhowextensivelytheyarerstintroduced. exercised,andthensetaside.theyarelistedhereinlinearorder,andwiththeir programming),withvaryingintensity,allalong. Thefollowinglistofitsmaintopicsreectstheexperiencesofthreeyearsof Weshouldremarkthatmostofthetopicsinthemodulearenotsimplytaught, (15hours):Introducingthebasiccomputationmodelofdata,variablesand (5hours):Introductorynotions,suchasalgorithms,algorithmicproblems, (9hours):Conditionalexecution;Booleanconditionswith`and'and`or' andtheexecutionprocess. (4hours):Aninitialdiscussionofthecorrectnessofalgorithms,mentioning (3hours):Modularization constructinganalgorithmfromsimplerones. connectives. input/output.emphasisisplacedonviewingasimpleprogramasasequence validinputs,correctnesswithrespecttoanalgorithmicproblem,andtesting ofvalue-changinginstructions. (12{15hours):Repetitiveexecutionofvariouskinds;counters;accumulators;exitconditions;nontermination. byrunningonsampleinputs. (8hours):Functions,emphasizingtheuseofafunctiontosolveasubproblem,andviewingafunctioncallasanewbasicinstruction. (3hours):Aninitialdiscussionofthetimeeciencyofalgorithms,including (12hours):One-dimensionalarrays. runningtimeasafunctionoftheinput,comparingrunningtimes,andworstcasetimebehavior. 21

22 (16{19hours):Asectionthatconcludesthe10thgradematerial,andincludesmorecomplexexamplesofalgorithmsandprograms,thenestingof controlstructures,andmore. 22