Rethinking Principal Effects on Student Outcomes

School principals are viewed as critical mechanisms by which to improve student outcomes, but there remain important methodological questions about how to measure principals' effects. We propose a framework for measuring principals' contributions to student outcomes and apply it empirically using data from Tennessee, New York City, and Oregon. We find that using contemporaneous student outcomes to assess principal performance is flawed. Value-added models misattribute to principals changes in student performance caused by factors that principals minimally control. Further, little to none of the variation in average student test scores or attendance is explained by persistent effectiveness differences between principals.