In an effort to reduce viral transmission, many schools are planning to reduce class size if they have not reduced it already. Yet the effect of class size on transmission is unknown. To determine whether smaller classes reduce school absence, especially when community disease prevalence is high, we merge data from the Project STAR randomized…

The California class size reduction program provided schools with cash rewards for K-3 classes of 20 or fewer students. I show how program rules made it possible for schools to save money by using mixed-grade classes to meet class size reduction obligations while maintaining larger average class sizes. I also show that this smoothing of students…