A sociocultural ontology forms the foundation for this grounded theory ethnography describing how teachers in a U.S. elementary school changed professional learning from a “training model” to a “situative model.” Findings answer the research question: How does the introduction of a situative model influence the process of teacher learning and professional development? A practitioner researcher stance and emic perspective facilitated an iterative analysis of 42 veteran teachers during the first-year implementation of a situative professional learning model called Teacher Communities of Learning (TCLs). Data collection included a repeated questionnaire, participant observations with field notes, and audio transcripts of TCL meetings. Formal and informal interviews provided opportunities for triangulation of data and theory development. ATLAS.ti assisted a constant comparative analysis process. Findings include a description of teachers’ participation in TCLs, influences on participation (e.g., roles, care, reflection), responses to TCLs among Suntree teachers, and shifts that occurred during the academic year as TCLs were introduced. The role of practitioner research in school and teacher change processes, the process of negotiation during situative learning, and differences in teachers’ roles and responses to TCLs are discussed. This research promotes a model for understanding how reflection and enaction account for teacher change and the importance of an ethic of care on formation of a professional community of learners.