Previous research has established the potential for achievement gains from attending smaller classes. However, large state-wide class-size reduction (CSR) policies have not been found to consistently realize such gains. A leading explanation for the disappointing performance of CSR policies is that schools are forced to hire additional teachers of lower quality to meet the new class-size requirements. This paper uses administrative data from an anonymous, diverse state to explore whether there were noticeable changes in the quality, measured by value-added to mathematics achievement, of newly hired teachers around the introduction of CSR. If so, were these changes large enough to account for the disappointing performance of the policy? The results suggest that while there was a modest fall in the relative average quality of newly hired teachers and those retained beyond their first year, this drop is not nearly large enough to explain the failure of CSR to produce sizeable achievement gains. Furthermore, schools facing CSR pressure saw similar falls in quality as those that did not, likely due to labor market competition forcing all schools along the effective teacher supply curve. Therefore, between-school differences in the quality of incoming teachers cannot explain the failure of previous quasi-experimental treatment-control comparisons to find achievement effects from statewide CSR. In addition to providing insight into CSR, the results are informative for assessing any potential intervention that may drastically increase the short-run demand for teachers.
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