Effect of class size on student achievement in the COVID-19 “new normal”

The COVID-19 pandemic implied measures, such as school closures at the outbreak of the pandemic, negatively affected children's human capital. However, in some places, the situation later resulted in a reduction in class sizes in order to avoid the spread of SARS-Cov-2 in schools. We take advantage of this unexpected event to evaluate the effect on school performance of a significant class size reduction implemented in Spain, when schools were reopened. We find a positive and significant effect of the class size reduction of 0.11 standard deviations on overall students' performance. Given the situation and nature of our data, we interpret our estimates as a lower bound for the true effect of the reduction in class size. We conclude that the reduction in class size served, on average, to at least compensate for the other negative effects on learning. Our findings also point out the importance of evaluating the quality of the new and inexperienced additional teachers that need to be hired when implementing a general reduction of class size.