Class Assignment and Peer Group Effects: Evidence from Brazilian Primary Schools

Students in Brazil are typically assigned to classes based on their age ranking in their school grade. I exploit this rule to estimate the effects on maths achievement of being in a class with older peers for students in fifth grade of primary school. Because grade repetition is widespread in Brazil, the distribution of age is skewed to the right and hence age heterogeneity is typically higher in older classes. I provide evidence that heterogeneity in age is the driving factor behind the large negative estimated effect of being in an older class. Information on teaching practices and student behaviour sheds light on how class heterogeneity harms learning.