OBJECTIVES: To evaluate the impacts of the expansion of an evidence-based full- and part-day early childhood development program on multiple indicators of school readiness, attendance, and parental involvement for a large cohort of low-income children. METHODS: This study involved the end-of-preschool follow-up of a nonrandomized, matched-group cohort of 2630 predominantly low-income, ethnic minority children who enrolled in the Midwest Child-Parent Centers (CPC) or alternative preschools in the fall of 2012 in 31 schools in Chicago, Illinois. The program provides comprehensive education, family support, and health services. In the preschool component assessed in this study, 1724 children aged 3 to 4 years in all 16 Chicago centers enrolled in the program. The comparison group included 906 children of the same age who participated in the usual preschool services in 14 matched schools. RESULTS: Relative to the comparison group who enrolled in the usual preschool services and adjusted for covariates, CPC participants had higher mean scores on all performance-based assessments of literacy (59.4 vs 52.4; P = .001), socioemotional development (57.0 vs 51.8; P = .001), and physical health (34.5 vs 32.1; P = .001). They also had higher ratings of parental involvement in school (5.3 vs 4.0; P = .04). Group differences also translated into higher rates of meeting national assessment norms. Program estimates were similar for children attending new and established CPCs and according to age, race/ethnicity, and family income status. CONCLUSIONS: The findings show that expansion of the program to new schools and more diverse populations is feasible and effective in promoting school readiness skills and parental involvement.