This case study describes the peer evaluation system the Maricopa County Educational Services Agency (MCESA) is using in the districts participating in its TIF 3 and TIF 4 grants. This brief first discusses the potential advantages and challenges of implementing peer evaluation and then describes the design and evolution of MCESA's peer evaluation process and what is currently known about its impact on teachers and school leaders. It concludes by presenting the lessons MCESA learned in operating the program since the 2012-13 school year.1 MCESA has been particularly thoughtful in designing a peer evaluation approach that fits the needs of its districts. It has successfully addressed most of the challenges of implementing peer evaluation. While the exact design of this program will not be applicable everywhere, MCESA has learned several lessons that could help other grantees design and implement peer evaluation programs that would further their grant's objectives.