Although literacy research has traditionally focused on content area and disciplinary literacies, in this study we argue for the importance of transdisciplinarity. We employed a participatory action research design to examine pre-service teachers' (PST) planning of a transdisciplinary math and music lesson to understand how conceptual framing of pedagogy and instructional practice can be shifted from content literacies to transdisciplinarity. Our area of inquiry focused on how PSTs' understanding of transdisciplinarity shifted as they planned, taught, and reflected on instruction and how these shifts were supported by others. We documented evidence of how the lesson progressed from disciplinary thinking to interdisciplinary, multidisciplinary, and transdisciplinary thinking throughout the planning process. We also documented how the process of planning, teaching, coaching, and reflecting provided PSTs with an opportunity to better understand the connections between transdisciplinarity and pedagogy.