In l975, a longitudinal evaluation was begun of the New York State Experimental Prekindergarten Program to determine its effects on children's cognitive and non-cognitive development. The population consisted of 5,000 disadvantaged 4-year-olds enrolled in the program. The study provides evidence that the program had a general effect, not restricted to grade level, on the children's knowledge of verbal concepts after they left the program. A sub-study of effects of staff development activities (designed to increase continuity of children's learning experiences) gave evidence that with appropriate follow-up in the primary grades, certain effects, most notably those in the quantitative domain, may persist into the primary grades. The program was most effective for children whose mothers had the least education. The more time parents spent participating in the program, the higher their children scored on measures of cognitive development. Children who were exposed the greatest amount of time to the program were rated higher by their teachers on task orientations, extraversion, and verbal facility. Perhaps most important of all, children who had participated in the prekindegarten program were more likely to make normal progress through the primary grades. (Author)