Teacher effectiveness varies substantially, yet principals' evaluations of teachers often fail to differentiate performance among teachers. We offer new evidence on principals' subjective evaluations of their teachers' effectiveness using two sources of data from a large, urban district: principals' high-stakes personnel evaluations of teachers,…

Better teacher evaluation should lead to better instruction and improved outcomes for students, but more accurate classification of teachers requires better information than is now available. Because existing measures of performance are incomplete and imperfect, measured performance does not always reflect true performance. Teachers who are truly…

Value-added models in education research allow researchers to explore how a wide variety of policies and measured school inputs affect the academic performance of students. Researchers typically quantify the impacts of such interventions in terms of "effect sizes", i.e., the estimated effect of a one standard deviation change in the…