The purposes of this study were to determine (1) the long-range effectiveness on children's cognitive and affective development of 1, 2, and 3 years of the Central Cities Early Childhood Education Program; (2) how long preschool intervention must be continued to significantly alleviate special problems of disadvantaged children; and (3) the optimum age to begin preschool intervention. Results indicate the program effectively helped children develop an adequate self-concept and social, emotional, motor, and physical skills for successful peer and teacher relations 2 and 3 years after their preschool experiences. Children maintained IQ gains measured by the Peabody Picture Vocabulary Test during preschool and 1 year later, and maintained gains made on the Slosson Intelligence Test 2 or 3 years after preschool. After 3 years of preschool, first grade entrants scored significantly higher on a school readiness test than classmates, but did not achieve as well as predicted by the end of first grade. Two years after the preschool program, children with 3 years of preschool made 1 year's gain on an achievement test but were below grade level on national norms. Intervention begun at age 3 and continued for 3 years is more beneficial than later intervention. (Author/DO)