The present study involved the evaluation of the effectiveness of four types of preschool programs on the educational development of lower and middle class children. Middle class children were exposed to "unit" and "cognitive" based preschool programs; lower class children were exposed to "day care" and Montessori programs. Comparison of the children's performances in cognitive, behavioral-social, sensory-motor, and language areas to appropriate control groups indicated that the type of program presented was not significant. However, preschool educational experience, irrespective of program, was significant in facilitating educational development. Furthermore, middle class children excelled beyond the lower class children. (Author)