Answers and Questions About Class Size: A Statewide Experiment

TLDR

The mechanisms behind the observed benefits of smaller class sizes remain largely unknown, warranting further investigation. The study randomized kindergarten students and teachers to small or large classes within each school, followed them for two years, and assessed reading and mathematics at the end of each grade using standardized and curriculum-based tests. Students in smaller classes showed significant gains in reading and mathematics, with minority students benefiting most, and a longitudinal analysis revealed continued superiority over peers in kindergarten and greater reading gains in the second year.

Abstract

A large-scale experiment is described in which kindergarten students and teachers were randomly assigned to small and large classes within each participating school. Students remained in these classes for 2 years. At the end of each grade they were measured in reading and mathematics by standardized and curriculum-based tests. The results are definitive: (a) a significant benefit accrues to students in reduced-size classes in both subject areas and (b) there is evidence that minority students in particular benefit from the smaller class environment, especially when curriculum-based tests are used as the learning criteria. A longitudinal analysis of a portion of the sample indicated that students in small classes outperform their peers in kindergarten classes of regular size and also gain more in reading outcomes during the second year. The question of why these effects are realized remains largely unanswered, but in light of these findings, is particularly important to pursue.