Class Size Reduction
Class size reduction produces positive effects in early grades, but is expensive and vulnerable to general equilibrium effects at scale.
Overview
The effect of class size on student achievement is one of the most heavily studied, yet persistently debated, topics in education policy. The intuitive appeal of smaller classes — more individualized attention, better classroom management — has made class size reduction a perennially popular policy proposal, despite mixed evidence on its cost-effectiveness.
Experimental and Quasi-Experimental Evidence
The strongest causal evidence comes from the Tennessee STAR experiment. Krueger's (1999) reanalysis found that students randomly assigned to small classes (13–17 students) outperformed those in regular classes (22–25 students) by approximately d = 0.22 in reading and d = 0.27 in math in kindergarten, with effects persisting through 4th grade and significantly larger for minority and low-income students. Angrist and Lavy (1999) exploited Maimonides' Rule in Israel as a natural experiment, finding significant positive effects. Fredriksson, Öckert, and Oosterbeek (2013) used a regression discontinuity design in Sweden to show that one fewer student per class raised adult earnings by approximately 3%.
Cost-Effectiveness and General Equilibrium Effects
The skepticism toward class size reduction has deep roots. Hanushek's (1986) influential meta-analysis of 147 educational production function studies found no systematic positive relationship between smaller classes and student achievement: of 112 estimates of teacher/pupil ratio effects, only 9 showed a statistically significant positive relationship, while 14 showed a statistically significant negative relationship. Despite positive findings from the STAR experiment, widespread implementation has proven problematic. Jepsen and Rivkin (2009) showed that California's massive class size reduction initiative yielded near-zero net benefits for disadvantaged students because the sudden demand for new teachers led wealthy districts to poach experienced teachers from poorer districts. Cross-national analyses (Wößmann and West, 2006) find inconsistent and generally small effects of class size across different education systems. Countries with large average class sizes (South Korea, Japan) consistently outperform countries with smaller classes on international assessments.
Class size reduction is popular but ranks poorly on cost-effectiveness metrics. Given the massive expense — estimated at $15,000–$20,000 per student per year for a reduction from 25 to 15 students — interventions like high-dosage tutoring are increasingly viewed as more efficient mechanisms for delivering individualized attention. Class size reduction is most beneficial in early grades, for disadvantaged students, and in contexts where teacher quality can be maintained during expansion.
Key Papers
- Angrist & Lavy (1999)Using Maimonides' Rule to Estimate the Effect of Class Size on Scholastic Achievement
- Fredriksson & Öckert & Oosterbeek (2013)Long-Term Effects of Class Size
- Hanushek (1986)The Economics of Schooling: Production and Efficiency in Public Schools
- Jepsen & Rivkin (2009)Class Size Reduction and Student Achievement: The Potential Tradeoff between Teacher Quality and Class Size
- Krueger (1999)Experimental Estimates of Education Production Functions
- Wößmann & West (2006)Class-Size Effects in School Systems Around the World: Evidence from Between-Grade Variation in TIMSS