Class-size reduction policies and the quality of entering teachers

Class-size reduction (CSR) policies have typically failed to produce large achievement gains. One common explanation is that CSR forces
schools to hire low-quality teachers. Prior studies of this hypothesis have
been hindered by poor data. Using different data, we find that hiring
quality did fall with state-wide CSR. However, this drop was temporary
due to attrition by the lowest performers. Furthermore, the drop was
similar for schools classified as treated and control for prior evaluations
of CSR. Therefore, differences in the quality of incoming teachers cannot
explain the estimated performance of CSR. This is consistent with hiring
spillovers in connected markets.