Are class size differences related to pupils' educational progress and classroom processes? findings from the institute of education class size study of children aged 5–7 years

Abstract Despite evidence from the USA that children in small classes of less than 20 do better academically there is still a vociferous debate about the effects of class size differences in schools, and considerable gaps in our understanding of the effects of class size differences. This article summarises results from the most complete UK analysis to date of the educational consequences of class size differences. The study had two aims: first, to establish whether class size differences affect pupils’ academic achievement; and second, to study connections between class size and classroom processes, which might explain any differences found. The study had a number of features that were designed to be an improvement on previous research. It used an ‘observational’ approach, rather than an interventionist one, in order to capture the nature of the relationship between class size and achievement across the full range of observed classes, and it employed a longitudinal design with baseline assessment to adjust for possible non‐random selection of children into classes. The study followed a large sample of over 10,000 children from school entry through the infant stage, i.e. children aged 4–7 years. It used multilevel statistical procedures to model effects of class size differences while controlling for sources of variation that might affect the relationship with academic achievement, and a multimethod research approach, integrating teachers’ judgements and experiences with case studies, and also carefully designed time allocation estimates and systematic observation data. Results showed that there was a clear effect of class size differences on children's academic attainment over the (first) Reception year. In the case of literacy, the lowest attainers on entry to school benefited most from small classes, particularly below 25. Connections between class size and classroom processes were examined and a summary model of relationships presented. Effects were multiple, not singular; in large classes there are more large groups and this presented teachers with more difficulties, in smaller classes there was more individual teacher contact with pupils and more support for learning, and in larger classes there was more pupil inattentiveness and off‐task behaviour. Results support a contextual approach to classroom learning, within which class size differences have effects on both teachers and pupils. It is concluded that much will depend on how teachers adapt their teaching to different class sizes and that more could be done in teacher training and professional development to address contextual features like size of class.