Recent New Leaders' research found principals are critical to teacher success in three ways: (1) developing teachers--working with teachers to improve skill and classroom practice; (2) managing talent--hiring, placing teachers, and monitoring performance; and (3) creating a great place to work--shaping schools into places where teachers want to stay. Principals who prioritized improving teacher effectiveness--and who were skilled at it--saw dramatic gains in student achievement. These findings suggest that investments in principal effectiveness are a strategic lever for effective teaching at scale. This policy brief provides recommendations that speak to the very specific role that policy has to play in fostering great principal actions that amplify great teaching. Recommendations are provided for the local, state, and federal levels. [For the full report, see ED585108. For the executive summary, see ED585109.]