We estimate the effect of class size on student performance in 18 countries, combining school fixed effects and instrumental variables to identify random class-size variation between two adjacent grades within individual schools. Conventional estimates of class-size effects are shown to be...

We employ a combination of school fixed effects and IV estimation to estimate the effect of class size on student performance in 18 countries. Using the random part of the class-size variation between two adjacent grades within individual schools allows us to identify causal class-size effects....