This report, one of several background papers for a comprehensive policy study of early childhood education, examines the effects of preschool experience on Illinois children from low income families. The 1980 U. S. Census for Illinois identified 81,959 preschool-age children (3 to 5 years old) from poverty-level families; 54 of these young children were not enrolled in a preschool program. A review of the literature in this paper focuses on factors which enable children to experience early success in school and which continue to have an effect on the quality of education a child receives in his later school years. Substantive descriptions of seven studies of preschool programs designed to serve children from low-income families are included. Highlighted are the outcomes of the early 1965 Project Head Start, the Follow Through program study in 1982, the 1978 study for the Educational Testing Service of Head Start programs, Cornell University's Consortium for Longitudinal Studies report in 1978, the still ongoing Illinois model program for the Early Prevention of School Failure Project, the 1982 Philadelphia School District study, and the Perry Preschool Project of 1984. A summary of these studies reporting preschool effects on various age groups of low income children shows that, during the preschool years, children demonstrate improved intellectual capacity, i.e., higher I.Q. scores. These initial gains, while not sustained beyond the second grade, appear to inhibit special education placement and give the children a short-term advantage in academic success during the first years of schooling. Throughout the elementary school years, the preschool participants demonstrate improved scholastic achievement and reduced frequency of special education placement. Finally, during the high school years and beyond, preschool participants have a lower rate of delinquency and/or criminal charges, a higher rate of high school graduation, and a higher rate of employment a year after graduation. (DST)