Context: Most studies of the long-term effects of early childhood educational interventions are of demonstration programs rather than large-scale public programs. Previous studies of one of the oldest federally funded preschool programs have reported positive effects on school performance, but effects on educational attainment and crime are unknown. Objective: To determine the long-term effectiveness of a federal center-based pre-school and school - based intervention program for urban low-income children. Design, Setting, and Participants: Fifteen-year follow-up of a nonrandomized, matched-group cohort of 1539 low-income, mostly black children born in 1980 and enrolled in alternative early childhood programs in 25 sites in Chicago, Ill. Interventions: The Chicago Child-Parent Center (CPC) Program (n=989 children) provides comprehensive education, family, and health services and includes half-day pre-school at ages 3 to 4 years, half- or full-day kindergarten, and school-age services in linked elementary schools at ages 6 to 9 years. The comparison group (n=550) consisted of children who participated in alternative early childhood programs (full-day kindergarten): 374 in the preschool comparison group from 5 randomly selected schools plus 2 others that provided full-day kindergarten and additional instructional resources and 176 who attended full-day kindergartens in 6 CPCs without preschool participation. Main Outcome Measures: Rates of high school completion and school dropout by age 20 years, juvenile arrests for violent and nonviolent offenses, and grade retention and special education placement by age 18 years. Results: Relative to the preschool comparison group and adjusted for several covariates, children who participated in the preschool intervention for 1 or 2 years had a higher rate of high school completion (49.7% vs 38.5%; P=.01); more years of completed education (10.6 vs 10.2; P=.03); and lower rates of juvenile arrest (16.9% vs 25.1%; P=.003), violent arrests (9.0% vs 15.3%; P=.002), and school dropout (46.7% vs 55.0%; P=.047). Both preschool and school-age participation were significantly associated with lower rates of grade retention and special education services. The effects of preschool participation on educational attainment were greater for boys than girls, especially in reducing school dropout rates (P=.03). Relative to less extensive participation, children with extended program participation from preschool through second or third grade also experienced lower rates of grade retention (21.9% vs 32.3%; P=.001) and special education (13.5% vs 20.7%; P=.004). Conclusions: Participation in an established early childhood intervention for low-income children was associated with better educational and social outcomes up to age 20 years. These findings are among the strongest evidence that established programs administered through public schools can promote children's long-term success.