Although early intervention programs have enjoyed popular and legislative support, little hard data exist on the long-term consequences of these efforts. This study examined the long-term effects of the Child-Parent Center (CPC) program in Chicago. Begun in 1967, the program operates out of 24 centers, located in proximity to the elementary schools they serve. The program's unique features include mandatory parental involvement and a single educational system spanning preschool through third grade. This study examined a 1986 cohort of almost 1,200 CPC children and a comparison group of low income children who were followed through age 15. The findings demonstrate that established large-scale early childhood programs can be successful for economically disadvantaged children and promote positive school adjustment and social behavior well into adolescence, and that contemporary programs can be just as effective as in earlier decades. The duration of program exposure was significantly associated with all measures of social competence. At least 2 years of post-kindergarten intervention were necessary to produce most lasting effects. However, early entry was crucial for long-term effects to occur. The most consistent long-term effects were to prevent grade retention and placement in special education and to promote school achievement and consumer skills. There were relatively modest effects on parent expectations for children's educational attainment, parent satisfaction with school, and parental involvement in school. Children in the highest poverty neighborhoods benefited more from participation than children in lower poverty settings. (Seven appendices include statistical data tables and a list of child-parent centers. Contains approximately 200 references.) (KB)