The effects of the Chicago Child Parent Center and Expansion Program were investigated for 6 social competence outcomes up to 2 years postprogram. A total of 1,106 low-income Black children were differentially exposed to school-based, comprehensive-service components for up to 5 or 6 years of intervention (preschool to Grade 3). Results indicated that the duration of intervention was significantly associated, in the expected direction, with reading and mathematics achievement, teacher ratings of school adjustment, parental involvement in school activities, grade retention, and special education placement. Analysis of 7 intervention and comparison groups revealed that participation in the follow-on intervention for 2 or 3 years significantly contributed to children's adjustment above and beyond preschool intervention and background factors. Both preschool and follow-on intervention meaningfully contributed to the cumulative effect of intervention.