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Version 1.1 – Updated August 2021

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: 8
  • Number of studies: 176
  • Number of students: 556,119
  • Number of effects: 1,158
  • Effect size: 0.18

Meta-Analyses

Meta-Analyses
Journal Title Author First Author's Country Article Name Year Published Variable Number of Studies Number of Students Number of Effects Effect Size
Educational Evaluation and Policy Analysis Glass & Smith USA Meta-analysis of research on class size and achievement 1997 Class size 77 520,899 725 0.09
The Elementary School Journal McGiverin et al. USA A meta-analysis of the relation between class size and achievement. 1999 Class size 10 0 24 0.34
Journal of the Royal Statistical Society: Series C (Applied Statistics) Goldstein, Yang, Omar, Turner, & Thompson UK 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 USA 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 0 328 0.31
European Expert network on Economics of Education Analytical Report, No. 33. Leuven & Oosterbeek Netherlands Class size and student outcomes in Europe 2018 Reducing class size by 10 16 0 16 0.10
Campbell Collaboration Filges, Sonne-Schmidt, & Nielsen Denmark Small Class Sizes for Improving Student Achievement in Primary and Secondary Schools: A Systematic Review 2018 Class size 6 0 9 0.11
Journal of Research in Reading Perlman, Fletcher, Falenchuk, Brunsek, McMullen, & Shah Canada A meta-analysis of the relationship between student attitudes towards reading and achievement in reading 2017 Class size in early childhood 3 5,780 3 0.06
KEDI Journal of Educational Policy Shin & Chung Korea Class Size and Student Achievement in the United States: A Meta-Analysis 2009 Class size 17 0 17 0.20
TOTAL/AVERAGE 176 556,119 1,158 0.18

Confidence

The Confidence is the average of these four measures, each divided into five approximately equal groups and assigned a value from 1 to 5 based on the following criteria:

  • Number of Meta-analyses
    • 1 = 1
    • 2 = 2–3
    • 3 = 4–6
    • 4 = 7–9
    • 5 = 10+
  • Number of Studies
    • 1 = 1–10
    • 2 = 11–50
    • 3 = 51–200
    • 4 = 201–400
    • 5 = 400+
  • Number of Students
    • 1 = 1–2,500
    • 2 = 2,501–10,000
    • 3 = 10,000–20,000
    • 4 = 20,000–100,000
    • 5 = 100,001+
  • Number of Effects
    • 1 = 1–100
    • 2 = 101–300
    • 3 = 301–600
    • 4 = 601–1,200
    • 5 = 1,200+
Confidences
Number of Meta-Analyses Number of Studies Number of Students Number of Effects Overall Confidence
Confidence Factor 4 3 5 4 4
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