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How Effective is Class Size Reduction?

BOULDER, CO (June 21, 2016) – Parents and teachers know that smaller class sizes allow more personalized attention and greater student learning. However, since the majority of a school’s budget is comprised of teacher pay and benefits, the cost of small classes can be a contentious issue for school administrators.

In a brief released today, The Effectiveness of Class Size Reduction, William Mathis explores the research on class size and finds that the clear conclusion to be drawn from reviewing high-quality peer-reviewed papers is that smaller classes are academically, socially, and economically beneficial. New light was cast on this perennial issue by a new study across 28 years and 28 states. Finance reforms directed toward small class sizes, longer school years and teacher salaries produced large gains in achievement, lifetime earnings and reduced adult poverty.

In the 1980s, the evidence of the impact of small class size on student academic achievement provided by the Tennessee Student/Teacher Achievement Ratio (STAR) experiment and its follow-up reports had an impact in the political arena. In the 1990s, annual evaluations of the Wisconsin Student Achievement Guarantee in Education (SAGE) reproduced the STAR results. Class sizes of 15, SAGE researchers found, had a significant impact on student test performance.

Class size reduction benefits all students; however, poor and minority students benefit most of all. Small classes can be expected to narrow the racial achievement gap by about one-third.

Despite claims to the contrary by some policymakers, Mathis concludes that reduction in class sizes may prove the most cost-effective school improvement policy overall. In Mathis’ view, money saved today by increasing class sizes will likely result in additional substantial social and educational costs in the future.

Dr. Mathis is Managing Director of the National Education Policy Center, housed at the University of Colorado Boulder School of Education. This brief is the one in a series of concise publications, Research-Based Options for Education Policymaking, that takes up a number of important policy issues and identifies policies supported by research. Each section focuses on a different issue, and its recommendations to policymakers are based on the latest scholarship.

Find William Mathis’s brief on the NEPC website at:

This policy brief was made possible in part by the support of the Great Lakes Center for Education Research and Practice ( 

The National Education Policy Center (NEPC), a university research center housed at the University of Colorado Boulder School of Education, produces and disseminates high-quality, peer-reviewed research to inform education policy discussions. Visit us at: