The PerW Prcsch~~ol Project is a longitudinal experiment designed to rc~e<br >cft~-cts of early intervention on disadvantaged children. Bc~un in Yps<br >Michig:m in 1962， the study comparcs an experimental group thai rccci<br >daily prcschool program (with weekly home visits) and a control grouI<br >received no intervention program.<br > This monograph reports the findings of the I crrs l rcschool Project lrc<br >beginning until subjects were 1S }ears old. In terms of the time span cove<br >goes beyond two previous mon~~graphs reporting the study( Weik:trt， l)~<br >l.awser， & ~ icgerink， 19"O; Wcikarl， Bond， & McNeil， 197g ). At this wrili~<br >study continues， with data being collected from ;rod about subjects at al<br > "11~c study x~as originally designed to test the straightR~rward hypothcs<br >oath interxlention has some po，sitivc eftcot on children. Almost two tic<br >later， a more complex analysis is called for， partly because of the broad al<br >data 1o be examined and partly because of greater cauti()tJsncss am~)l<br >pul~lic about programs which .~-ck to alleviate the eftcots of povcrt} . 11~c<br >findings arc prc~ nted in terms of a set ofintercomlccted pathxvays dcfini<br > effccts of early intervention over time. The longitudinal stud} of<br > intervention requires the guidance of a conceptual framework As lhc yt<br > hv and the data set grows in size and complexity， this conceptthd |r，u]lev<br > n~:cdcd to determine the nature of data to bc collected as wcll as aid<br > interpretation of findings.<br > A truly longitudinal study is not likcly to simply lest :l set ofap~f+;~f h}l+o<br > in the traditional scientific manner. l]le investigators， the scientific par:<br > which guide them， and the cuhural mood :ill change over time. ll~en l(<br > findings that appear during the earl} part of the study prm idc im<br > feedback to shape the later par3 of the study， even [o delerminc whcthc<br > the study is to corltinuc.<br > ll~e Pero Preschool Project began as a local evaluation t}.)r ;l local au(<br > Now it is a pivotal study on the long-term effects， and even thc valuc， t<br > educational intervention， lls audicncc is national and international. I;ortu<br > there havc been several other longitudinal sit，dies ()f early inter~<br > programs. But the PerD Project appears to bc the only Iongiludiual s~<br > disadvantaged children meeling two basic criteria: ( 1 ) an cxpcrimcnlal<br > with experimental and control groups assigned on an esscntiall} randor<br > and ( 2 ) an early intervention program of daily preschool education and<br >