Skip to Content
Visible Learning™
Visible Learning MetaX™
Version 1.4 – Updated February 2026

Reducing class size

Overview

  • Influence: Reducing class size
  • Domain: Classroom
  • Sub-Domain: Class composition effects
  • Potential to Accelerate Student Achievement: Likely to have a small positive impact
  • Influence Definition: Reduces the number of students in the class often with the aim of increasing the number of individualized student-teacher interactions to improve student learning.

Evidence

  • Number of meta-analyses: 9
  • Number of studies: 238
  • Number of students: 564,964
  • Number of effects: 2,934
  • Weighted mean effect size: 0.14
  • Robustness index: 4

Meta-Analyses

Meta-Analyses
Journal Title Author Article Name Year Published Variable Number of Studies Number of Students Number of Effects Effect Size
Educational Evaluation and Policy Analysis Glass & Smith Meta-analysis of research on class size and achievement 1979 Class size 77 520,899 725 0.09
Elementary School Journal McGiverin, Gilman, & Tillitski A meta-analysis of the relation between class size and achievement. 1989 Class size 10 NA 24 0.34
Journal of the Royal Statistical Society. Series C: Applied Statistics Goldstein, Yang, Omar, Turner, & Thompson Meta-analysis using multilevel models with an application to the study of class size effects 2000 Class size 9 29,440 36 0.20
Educational Evaluation and Policy Analysis Bowne, Magnuson, Schindler, Duncan, & Yoshikawa A Meta-Analysis of Class Sizes and Ratios in Early Childhood Education Programs: Are Thresholds of Quality Associated With Greater Impacts on Cognitive, Achievement, and Socioemotional Outcomes? 2017 Class size in early childhood 38 NA 328 0.31
Report Leuven & Oosterbeek Class size and student outcomes in Europe 2018 Reducing class size by 10 16 NA 16 0.10
Campbell Collaboration Filges, Sonne-Schmidt, & Nielsen Small Class Sizes for Improving Student Achievement in Primary and Secondary Schools: A Systematic Review 2018 Class size 6 NA 9 0.11
KEDI Journal of Educational Policy Shin & Chung Class Size and Student Achievement in the United States: A Meta-Analysis 2009 Class size 17 NA 17 0.20
Campbell Systematic Reviews Dalgaard, Bondebjerg, Klokker, Viiholt, & Dietrichson Adult/child ratio and group size in early childhood education or care to promote the development of children aged 0–5 years: A systematic review.  2022 Class size in early childhood 3 14,625 12 -0.04
MetaArXiv Preprints Opatrny, Havranek, Irsova, & Scasny Class Size and Student Achievement: A Modern Meta-Analysis 2023 Class size 62 NA 1,767 0.08
TOTAL/AVERAGE 238 564,964 2,934 0.15
Back to top