This report presents results of Tennessee's 4-year longitudinal class size project: Student Teacher Achievement Ratio (STAR). The study analyzes student achievement and development in three class types: small classes with 13-17 students per teacher; regular classes with 22-25 students per teacher, and regular classes with 22-25 students per teacher assisted by a full-time teacher aide. Project STAR followed students from kindergarten through third grade, starting in 1985-1986 and ending in 1988-1989. Sections of this report concern: (1) background and purpose of the study; (2) study design; (3) descriptive data and teacher effectiveness; (4) primary findings; (5) the longitudinal analysis; (6) teacher in-service training; (7) effects of class size on classroom processes; (8) additional findings; (9) the cost-effectiveness of reducing class size or adding aides; and (10) a summary of the study. Numerous tables and figures supplement the text. Appended materials concern related legislation and literature, data processing issues, findings on teacher effectiveness, longitudinal tables across grades, student socioeconomic status, Project STAR Abstracts, and the relation of teacher aides to student performance. Citations number 156. (RH)