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, that negatively affected children's human capital. However, in some places, the situation later brought a reduction in class sizes, in order to avoid the spread of SARS-Cov-2 at schools. We exploit this unexpected event to evaluate the effect on school performance of a sizable 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. Our conclusion is that the reduction in class size served, on average, to at least compensate the other negative effects for learning. Our findings also point out at the importance of evaluating the quality of the new and unexperienced additional teachers that need to be hired when implementing a general reduction of class size.