Morgan S. Polikoff and Matthew Di Carlo write in The Washington Post’s The Answer Sheet blog: One of the primary policy levers now being employed in states and districts nationwide is teacher evaluation reform. Well-designed evaluations, which should include measures that capture both teacher practice and student learning, have great potential to inform and improve the performance of teachers and, thus, students. Furthermore, most everyone agrees that the previous systems were largely pro forma, failed to provide useful feedback, and needed replacement. The attitude among many policymakers and advocates is that we must implement these systems and begin using them rapidly for decisions about teachers, while design flaws can be fixed later. Such urgency is undoubtedly influenced by the history of slow, incremental progress in education policy. However, we believe this attitude to be imprudent. The risks of excessive haste are likely higher than whatever opportunity costs would be incurred by proceeding more cautiously. Moving too quickly gives policymakers and educators less time to devise and test the new systems, and to become familiar with how they work and the results they provide.