The "Race to the Top" competitive grant program initiated a wave of teacher evaluation reform, which scholars and policymakers have long identified as critical to improving teacher quality and student performance. State boards of education (SBEs) and state education agencies (SEAs) took different approaches to these reforms, and as a result, clear tension has emerged between some states' desires to let districts select or adapt evaluation instruments that are best suited to their particular circumstances. Because teacher evaluation systems are still a work in progress, it is vital that school leaders and administrators continue to solicit feedback, learn from their mistakes, and make improvements. In that spirit, the author conducted comparative case studies on the implementation of teacher evaluation reforms in six "early adopter" states: Colorado, Delaware, New Jersey, Pennsylvania, Rhode Island, and Tennessee. Their experiences reveal some of the key challenges and adaptations in implementing new teacher evaluation systems, as well as recommendations that can inform the efforts of other states going forward.