This paper describes the scope and findings of a separately published comprehensive review of research on optimum age of entry into first grade, covering the literature from 1915 to 1976. (Not included was research on reading, the gifted, mentally retarded, and materials in popular journals.) Findings noted the inadequacy of chronological age as a predictor and indicated an optimum mental age of 6 1/2 years for most cases. Also noted: disadvantage to the child younger than his peers; developmental patterns in visual ability to deal with the printed word; variations of as much as five years in reading readiness at age 6; ineffectiveness of early intensive drill in learning to read; correlation between maturity and learning to read; higher incidence of social, emotional and scholastic problems among younger children than among comparable children a year older; benefits from additional kindergarten experience; and need for entry decisions on an individual basis. The findings and conclusions are listed under separate headings for the following criteria: chronological age, mental age, IQ, sex, physiological development, social and emotional development, and relative age. Effects of early admission are described, and early entry and reading are discussed briefly. (BF)