The study investigated the relation between participation in the Child-Parent Center and Expansion Program during preschool to third grade and measures of adolescent delinquency for low-income, mostly black youths in the Chicago Longitudinal Study. Based on analyses of 1,262 program and comparison-group children, duration of program participation (0 to 6 years) and extensive participation in the program were significantly associated with lower rates of school-reported delinquency infractions at ages 13 and 14. Extended program participation was only marginally associated with a lower rate of delinquency infractions over ages 12 to 16. Preschool participation alone had no systematic relation with delinquency but was marginally associated with delinquency reports at ages 15 and 16. Reduction in school-reported delinquency was a consequence of less frequent school mobility and postprogram parent involvement in school. Tables, figures, notes, references