Proficiency-based learning systems are becoming more common across the United States, yet few pre-service mathematics teachers have experienced this type of system in the classroom themselves. Teacher education courses are one opportunity for pre-service teachers to experience proficiency-based learning; however, we know little about the impact this type of experience might have. This study examines the experiences of six pre-service teachers in a secondary mathematics methods course implementing proficiency-based learning. Results show that the pre-service teachers experiences centred on four key affordances of the system (flexibility, multiple opportunities to demonstrate learning, awareness of progress and process, and awareness of gains in pedagogical content knowledge) and that they also identified challenges to its implementation.