Ten years ago, the reform of teacher evaluation was touted as a mechanism to improve teacher effectiveness. In response, virtually every state redesigned its teacher evaluation system. Recently, a growing narrative suggests these reforms failed and should be abandoned. This response may be overly simplistic. We explore the variability of New York City principals' implementation of policies intended to promote teaching effectiveness. Drawing on survey, interview, and administrative data, we analyze whether principals believe they can use teacher evaluation and tenure policies to improve teaching effectiveness, and how such perceptions influence policy implementation. We find that principals with greater perceived agency are more likely to strategically employ tenure and evaluation policies. Results have important implications for principal training and policy implementation.