Peer Assistance and Review (PAR) is a promising program to improve the teacher evaluation system and teaching quality more broadly. Under PAR, an innovative approach that uses expert teachers to conduct regular evaluations for novice teachers and underperforming veterans, districts can focus attention on instructional quality, retain the most effective teachers, and dismiss teachers who are not contributing to student learning. Because PAR places some evaluation responsibility on peers and requires a team of teachers and administrators to manage the process, the program is challenging to implement. It holds great potential, however, for improving teacher quality. The authors of this report sought to expand what is known about PAR by examining the program in seven districts across the country, focusing on districts that provide both peer assistance and peer review, where teachers support and evaluate their colleagues in a process that can lead either to continued employment or to dismissal. Approximately 25 individuals were interviewed in each district, including the superintendent or associate superintendent, the teachers union president, other administrators and union representatives, principals, and the expert consulting teachers who work in the program on a daily basis. The authors present what they have learned about designing and implementing an effective PAR program. This report describes PAR and its promise for improving teacher quality, discusses key challenges and common problems districts face as they adopt PAR, suggests what districts can do to implement PAR effectively and ensure that this potential is realized, and offers recommendations for federal and state policymakers who seek to support the development and success of PAR. The following is appended: Summary details of Peer Assistance and Review programs studied. Contains endnotes. [Partial support for this work was provided by Katharine and Al Merck.]