assignment. Johnson and Papay provide a simple, yet rich analytical framework that allows one to clearly identify the dimensions on which pay-for-performance plans differ. Their framework centers on the three most important questions districts must answer when designing such a plan: (1) which measures will be used in assessing performance -- standardized tests, professional evaluation, or a combination of both; (2) whether to identify top performers using relative rankings or a fixed standard; and (3) whether to provide awards at the individual or group (e.g., school) level. Each of these critical decisions affects teacher incentives in unique, often conflicting, ways. Building upon these three dimensions, Johnson and Papay classify 12 main "types" of pay-for-performance programs, each with its own strengths and weaknesses. Although the design elements of a pay-for-performance scheme play a vital role in its success, a variety of other factors, and in particular the local context and process of implementation, also matter a great deal. Johnson and Papay complement their theoretical discussion with illustrative examples of pay-for-performance programs in four large, urban districts -- Houston, Texas; Minneapolis, Minnesota; Charlotte-Mecklenburg, North Carolina; and Hillsborough County, Florida -- all of which provide substantial awards for teacher performance. These four districts have all been at the forefront of teacher pay reform, and have committed substantial amounts of money to performance bonuses. Notably, none of their plans is focused on a single measure of student performance. Rather, each district incorporates several complementary programs in their overall compensation strategy. Each district also includes