In this article, Jeremy Sullivan explores the history of teacher evaluations in Montgomery County, Maryland. He describes how, over the course of three decades, the Montgomery County Education Association (MCEA) established itself as a strong and powerful professional association and leveraged its power to institutionalize a more collaborative approach to teacher evaluations in the county. Drawing largely on archival data from educational organizations in Montgomery County, Sullivan shows how the MCEA and its member teachers objected to evaluation mechanisms they considered unfair and ineffective. He then outlines the process through which the MCEA worked together with administrators to develop the Peer Assisted Review program. Today this program, jointly run by MCEA and the school system, enjoys widespread support in the county and serves as an example of how teachers and their unions can partner with administrators to work together toward the goal of improving teaching and learning in public schools.