This review of research, part of the Illinois State Board of Education's Early Childhood Education Policy Study, focuses on issues related to potential state funding for full-day kindergarten and changes in the age at which children enter kindergarten. Specifically addressed are the following issues: (1) a review of the legislative background on initial school entry, (2) research on age as a factor related to successful school entry, (3) the effect of raising the school entry age, and (4) the application of delayed school entry age to Illinois children. Since chronological age is the most administratively convenient criterion used to determine eligibility for school entry, the first section on legislative background provides a table showing the variability of cut-off dates for kindergarten entry for forty states. The second section dealing with research on age as a criterion for initial school entry argues for an acknowledgement that a child's developmental age may be different from his/her chronological age. Included in this section are discussions on delaying the child's entrance into school and on enrolling the child in school at a particular age. An extensive review of the research on entry age focuses on factors related to the prediction of initial academic success of children entering kindergarten or first grade. These factors include chronological age, sex differences, socioeconomic status, intelligence, preschool experiences, social adjustment, and birth order of children. The third section debates the issues of whether raising the age for initial school entry helps to eliminate school failure by giving younger children a chance to mature. The final section identifies resultant problems stemming from delayed school age entry for Illinois children. The paper concludes that research literature does not support the raising of school entry age. (DST)