Class Size and Student Achievement: Experimental Estimates of Who Benefits and Who Loses from Reductions

Class size proponents draw heavily on the results from Project STAR to support their initiatives. Adding to the political appeal of these initiative are reports that minority and economic disadvantaged students received the largest benefits. To explore and truly understand the heterogeneous impacts of class size on student achievement requires more flexible estimation approaches. We consider several semi and nonparametric strategies and find strong evidence that i) higher ability students gain the most from class size reductions while many low ability students do not benefit from these reductions, ii) there are no significant benefits in reducing class size from 22 to 15 students in any subject area, iii) no additional benefits from class size reductions for minority or disadvantaged students, iv) significant heterogeneity in the effectiveness of class size reductions across schools and in parental and school behavioural responses.