Most teachers and the public believe that children in kindergarten and the primary grades benefit from small classes because of children's need for individualized instruction and teacher attention. This report, part of a comprehensive policy study of early childhood education, presents a review of the research on the effect of class size on student outcomes, including achievement and adjustment to school. Topics covered include the following: (1) child development theory, (2) class size research, (3) a review of practices in South Carolina, Florida, and Indiana (4) a review of current Illinois statutes and practices, and (5) a summary of the findings in terms of policy implications for the Illinois State Board of Education. A review of the mandates for class size in the School Code of Illinois (1983) is given and tables provide comparisons between grades and types of programs. Data on kindergarten/primary class sizes of three selected states, South Carolina, Florida, and Indiana, is highlighted because of the different methods used in these states to achieve lower student/teacher ratios. A table in the appendix summarizes the recommended class sizes for kindergarten through third grade for all fifty states. In conclusion, this review shows that there is general agreement that at the primary grades smaller classses facilitate learning and that class size must be sufficiently small - at least below 20 - for significant benefits. (DST)