Graduate teaching assistants (GTAs) influence undergraduate STEM students' learning and experience because they teach most lab sections across STEM disciplines. Despite GTAs' central role in lab teaching, their training is often focused on policies and expectations, rather than teaching effectively. In this study, we took a community of practice (CoP) approach to learning and facilitated a semester-long, pedagogy-focused CoP to address the lack of pedagogical development and support for GTAs. Our purpose was to collect, describe, and develop our understanding of the experiences of GTAs participating in our CoP while teaching reformed undergraduate exercise physiology labs. CoP members completed an asynchronous, SoTL-informed micro-course focused on evidence-informed teaching practices and active student learning support, which was then debriefed at the first CoP meeting. Each subsequent weekly meeting featured 30 minutes of CoP members reflecting on, discussing, and helping each other improve their teaching practices. At the end of the semester, we conducted semistructured interviews with GTAs to learn about their experiences in the CoP and teaching. We found reflecting on and talking about their teaching was a novel experience for GTAs. They also described implementing teaching practices that were new to them, exercising autonomy, developing confidence, approaching teaching philosophies, and their experiences with psychological safety. Our findings suggest facilitating weekly reflection on teaching in a CoP can provide GTAs with opportunities to develop their teaching practices in meaningful, practical, and (sometimes!) enjoyable ways.