Many existing teacher evaluation and reward systems do not capture variation in teachers' ability to improve student performance on standardized tests. Improved access to longitudinal data systems that link teachers to students facilitates the development of systems that incorporate student achievement gains into teacher evaluations. However, two important challenges remain: generating valid estimates of teachers' contributions to student learning and including teachers who do not teach subjects or grades that are tested annually. In their analysis of the systems of three districts and two states that have begun or are planning to incorporate measures of student performance into their teacher evaluations, the authors examine how the five profiled systems are addressing assessment quality, evaluating teachers in nontested subjects and grades, and assigning teachers responsibility for particular students. The authors also examine what is and is not known about the quality of various student performance measures used by school systems and offer recommendations to policymakers about approaches to consider when incorporating student achievement measures into teacher evaluation systems. Individual chapters contain footnotes. (Contains 6 tables and 5 footnotes.) [Funding for this paper was provided by the Center for American Progress.]