As part of a longitudinal study of the New York State Experimental Prekindergarten Program, the effect of degree of parental involvement in the program on children's cognitive development was examined. Parent involvement included employment in the program, school visits, home visits by school personnel, group meetings, and incidental contacts such as telephone calls. Degree of involvement ranged from 0 to 200 hours. Three kinds of cognitive development were examined: (1) general reasoning, measured by the Walker Readiness Test for Disadvangated Children; (2) school related knowledge and skills, measured by the Cooperative Preschool Inventory; and (3) knowledge of verbal concepts, measured by the Peabody Picture Vocabulary Test. Results showed that parent involvement had a favorable effect on all three kinds of cognitive development. The effects were found regardless of the child's age, mother's education, or family income. For general reasoning and school related knowledge and skills, the effects were also found, regardless of the child's score on the same test at the beginning of prekindergarten. For knowledge of verbal concepts, however, the effect of parent involvement tended to be greater for children who were initially lowest in knowledge of verbal concepts. (Author/SS)