Chetty, RajFriedman, JohnRockoff, Jonah E.2017-03-092014Chetty, Raj, John N. Friedman, and Jonah E. Rockoff. 2014. Measuring the Impacts of Teachers I: Evaluating Bias in Teacher Value-Added Estimates. American Economic Review 104, no. 9: 2593–2632. doi:10.1257/aer.104.9.2593.0002-8282http://nrs.harvard.edu/urn-3:HUL.InstRepos:30749073Are teachers' impacts on students' test scores ("value-added") a good measure of their quality? One reason this question has sparked debate is disagreement about whether value-added (VA) measures provide unbiased estimates of teachers' causal impacts on student achievement. We test for bias in VA using previously unobserved parent characteristics and a quasi-experimental design based on changes in teaching staff. Using school district and tax records for more than one million children, we find that VA models which control for a student's prior test scores exhibit little bias in forecasting teachers' impacts on student achievement.en-USJournal Article2017-03-0910.1257/aer.104.9.2593