The effect of primary school size on academic achievement

Evidence on optimal school size is mixed. We estimate the effect of transitory changes in school size on the academic achievement of 4th- and 5th-grade students in North Carolina using student-level longitudinal administrative data. Estimates of value-added models that condition on school-specific linear time trends and a variety of teacher-by-school, student, and school-by-year fixed effects suggest that on average, there is no causal relationship between school size and academic performance. However, two subgroups of interest are significantly harmed by school size: socioeconomically disadvantaged students and students with learning disabilities. The largest effects are observed among students with learning disabilities: a ten-student increase in grade size is found to decrease their math and reading achievement by about 0.015 test-score standard deviations.