Socioeconomic Status and Class Size in South African Secondary Schools

The reduction of class size is frequently argued to be a relatively simple, cost-effective way to improve learner outcomes in a wide array of contexts. However, methodological concerns regarding the appropriate use of observational data and endogeneity have led to a lack of consensus on this relationship in the literature. In the South African context, most studies which use observational data conclude that on average, greater class sizes are associated with poorer educational outcomes. However, given the country's well-documented bimodal education system, it is plausible to believe that such a relationship may depend on where learners finds themselves in the system. Specifically, given that class size is highly correlated with other measures of school quality, one may not find a significant relationship once such characteristics are accounted for. In this light, this paper merges newly available, school-level data from the 2017/18 School Monitoring Survey with external administrative data to investigate whether the relationship between secondary school class size and learner outcomes varies by school socioeconomic status. Using several learner outcome measures, the findings suggest that although extreme class sizes are concentrated in poorer schools, class size is only negatively associated with learner outcomes in wealthier schools. This does not imply that class size does not matter. Rather, variation in class size appears to be merely indicative of other important factors in poorer quality schools which influence learner outcomes. This suggests that a class size reduction policy may only be effective once other factors relating to school quality are addressed.