This document reviews the research literature concerning class size and related issues raised by the research. The literature is divided into major areas of concern: lack of a consistent definition, criterion to be measured, the relationship between class size and method of instruction, teachers' and pupils' attitudes on class size, class size and the behavior of pupils, review of class size studies by researchers at Columbia University, different interpretations of class size literature, and flexible policies. The summary indicates inconclusive findings; however, five factors affecting optimum class size were stressed. These factors include the criteria of success, the original class size, the subject being taught, whether or not the teacher can exploit the potential of smaller classes by using an appropriate method of instruction, and the teachers' feelings and attitudes. A 20-item bibliography is included. (MJM)