This report presents the results of a study from July 1965 to July 1969 on the effects of year-long prekindergarten programs for disadvantaged children involving eight school districts in New York State and approximately 1,800 children. The study focused on factors which the schools considered important and major objectives of their programs. These were intelligence, language, self-concept, and physical development. The study was a true experimental design with two replications. The basic data were collected by individualized tests and measurements (pretest and posttest) for the prekindergarten year for three waves of children. Posttesting was completed in the follow-up years. Reports and ratings by teams of observers, as well as teachers and program directors, were made in each of the three years. Each child's parent was interviewed. The cognitive programs were able to close some of the gap between disadvantaged and nondisadvantaged children. However, the difference that remained exceeded the difference overcome. Further, the results were achieved only by the cognitive-oriented programs, and not by the nursery-oriented or early childhood-oriented programs. (JM)