Nationwide, schools are implementing ambitious evaluation policies meant to improve education by holding teachers accountable and supporting their development. Seeking to learn whether and how evaluation policy could serve both purposes, we explored implementation of standards-based evaluation in six high-poverty schools of one urban district. Teachers widely said they wanted evaluation to provide both accountability and development. However, only one principal used evaluation to achieve both purposes. Four principals responded perfunctorily to the policy and achieved neither purpose. The sixth principal used evaluation primarily to dismiss teachers. We examine differences in implementation and their implications for policy, practice, and research.