The class size question in primary schools: policy issues, theory, and empirical findings from the Netherlands

Primary schools in the Netherlands are autonomous in their decisions on grouping of pupils, and therefore on class size matters, because the state may not interfere in pedagogical-didactical issues according to the constitution. Surveys indicate that both across as well as within schools (across grades) class sizes consequently vary quite a lot. Capitalizing on this situation, a randomly drawn sample of 416 schools was used to collect data on class sizes and pupil achievement in grades 2, 4, 6 and 8. Social-ethnic status, IQ and gender also were examined. Using multi-level statistical models the strongest size effects were obtained in grade 2 in classes below 25 and above 35. Interaction effects between socio-ethnic status, sex and IQ with class size on achievement showed inconsistent trends. In three out of ten cases the achievement gap widened with decreasing class size.