This review of research connected to Project Student Teacher Achievement Ratio (STAR) is a summary of the project's ongoing work in the form of a letter from researchers to a hypothetical colleague. Project STAR has investigated the effect on student achievement and development of small classes in the primary grades (K through 3). A research consortium of four universities and the State Education Agency was formed to conduct and monitor the study with the aid of an advisory panel and outside consultants. Forty-two districts and 79 schools (later 76) participated. Three major subsidiary studies have built on STAR: (1) the Lasting Benefits study that tracks students; (2) Project Challenge, a policy application of small classes in 16 low-performing school systems; and (3) the Grade 4 (and eventually Grade 8) participation study. The database established for STAR, which now includes about 9,000 students randomly assigned to small-class, regular-class, and regular-class with aide conditions, is serving as the basis for other research, including examinations of achievement, racial differences, the interaction of school size and class size, and other state initiatives. Three appendixes present tables of research design, analysis of variance for cognitive outcomes, and rankings of Challenge districts. (Contains 8 tables and 33 references.) (SLD)