Education officials often use one assessment system both to create measures of student achievement and to create performance metrics for educators. However, modern standardized testing systems are not designed to produce performance metrics for teachers or principals. They are designed to produce reliable measures of individual student achievement in a low-stakes testing environment. The design features that promote reliable measurement provide opportunities for teachers to profitably coach students on test-taking skills, and educators typically exploit these opportunities whenever modern assessments are used in high-stakes settings as vehicles for gathering information about their performance. Because these coaching responses often contaminate measures of both student achievement and educator performance, it is likely possible to acquire more accurate measures of both student achievement and education performance by developing separate assessment systems that are designed specifically for each measurement task.