Using communities of practice as a theoretical framework, the present study explored seven infant and toddler teachers’ professional learning in the context of weekly co-planning meetings with preservice teachers in four classrooms over one semester. Data sources included semi-structured interviews, observations, video-recordings, documents, and fieldnotes. The findings show that the teachers considered co-planning as crucial to their professional development. During co-planning, the teachers gained multiple perspectives through collective discussions; engaged in critical reflection; created new ideas of practice collaboratively; and enhanced their sense of professionalism. In addition, the preservice teachers were catalysts for the teachers’ reflection. The discussion highlights co-planning as a vehicle for sustaining a culture of reflective practice and collaborative inquiry; an opportunity to co-construct new knowledge and practice; and a space where teacher autonomy, collaboration, and experiential learning intersect to empower teachers in professional learning. Lastly, the study discusses ways to honor and support infant and toddler teachers’ professionalism. (author abstract)