Professional opinion and major research studies on the recommended sizes for school and school districts are summarized in this review. Definitive recommendations are not attempted, but the review does provide educational decision-makers with an insight into the thinking of others on these questions. The first section of the two-part study reviews research and opinion dealing with attempts to define an ideal size for school buildings at various intructional levels. Aspects of the school size question examined are the size of existing schools using the latest data available; local school system guidelines on school size; a review of research related to the size of elementary, middle, junior high, and senior high schools; literature on minimizing the shortcomings of schools that are too small or too large; and suggestions in recent professional literature for eliminating underutilization of schools as a result of enrollment declines. The second section examines research and opinion on the size of intermediate and local school disctricts. Although the greater number of documents deal with school size recommendations, the larger portion of recent research data focuses on school district size. (Author/MLF)