Nonlinear class size effects on cognitive and noncognitive development of young children

We estimate the nonlinear impact of class size on student achievement by exploiting regulations that cap class size at 20 pupils per class in kindergarten. Using student-level information from a previously unexploited large-scale census survey of kindergarten students, this study provides clear evidence of the nonlinearity of class size effects on both cognitive and noncognitive measures. While the effects are largest on cognitive development, class size reductions also improve social competence and communication skills in small classes of fewer than 15 students. Above that threshold, the impacts of class size reduction are limited. We also find stronger effects for students in disadvantaged areas. These findings suggest that sizeable class size reductions targeted at disadvantaged areas would achieve better results than a marginal reduction across the board, and even that large reductions in a limited number of classes could be financed by marginal increases in the vast majority of schools not experiencing high poverty rates.