The Maryland State Department of Education undertook a longitudinal study of the Extended Elementary Education Prekindergarten Program (which covers prekindergarten through grade 3) in order to examine the school performance of program participants and a comparable nonpreschool group. The study: (1) investigated effects of prekindergarten on participants' school performance; (2) determined whether prekindergarten participation improved economically disadvantaged children's performance to a level comparable to that of children from a variety of socioeconomic backgrounds; and (3) looked for sustained positive effects. Subjects were 356 prekindergarten graduates and 305 nonprekindergarten students. Demographic data about students' family life and preschool experiences was collected, and prekindergarten participation was assessed by means of four outcome measures of school progress and academic achievement. Results showed prekindergarten participants less likely to be classified as at risk, assigned to special education classes, or retained. They also scored significantly better on reading, language arts, and mathematics portions of the California Achievement Test (CAT) in grades 3, 5 and 8. While these differential gains in reading and language arts remained constant, the prekindergarten group's advantage in mathematics increased as these students progressed from grade 3 to grade 8. Throughout their eight years of schooling the prekindergarten group remained constantly close, but slightly below the average achievement level of the entire student population of the State. (SAK)