Class size reduction policy: Evaluating the impact on student achievement in California

California is spending {dollar}1.5 billion annually on its early elementary Class Size Reduction Program. This study evaluates the relationship between class size and student achievement for this California policy. A key motive behind the adoption of the policy was to raise test scores. A review of the pertinent literature and examination of preliminary findings from California point to the need for a detailed analysis of mathematics achievement in order to examine the link between class size reduction and improved academic performance as measured by the state mandated Stanford Achievement Test, 9th Edition.; A synthesis of empirical studies and further theoretical analyses provides expectations for the magnitude of the effect of class size reduction on student achievement and the specification of causal mechanisms. Five hypotheses were tested using data from over 11,000 students, nearly 700 teachers and classrooms, and over 70 schools from seven urban, suburban, and rural school districts from the first three years of implementation in California. Statistical analyses using hierarchical linear models support the propositions that early socialization is responsible for the achievement levels in mathematics associated with class size reduction experiences and that the easier classroom management in a reduced size class also contributes to gains in student achievement. At the classroom level, reduced size classes bring students who would otherwise be outlying performers along with the class as a whole, and possibly narrow the dispersion of achievement, making outcomes more uniform. Unfortunately, there is every reason to believe that a good portion of the achievement benefits of class size reduction is lost after students return to larger classes.; At the cost of {dollar}1.5 billion per year, the modest immediate return to student achievement in California and the smaller lasting benefit suggest that class size reduction is rather inefficient, even if it is effective. There is no indication that the racial/ethnic achievement gap closes as a consequence of the program. Research should be extended to inquire if the enormous expense of class size reduction is being recouped in such ways as restoration of public confidence, teacher willingness to embrace the demands of standards and accountability, long-term investment returns (future careers and schooling), or student identification with democratic pluralism and productive economic participation.