This paper focuses on the discourse of teachers and instructors in a TEAMS (Teaching Exploratively for All Mathematics Students) professional development (PD) setting and on the discursive mechanisms that afford such learning. We conceptualize learning in this PD as a change in a teacher's pedagogical discourse--from alignment with Delivery Pedagogical Discourse (DPD) to alignment with Explorative Pedagogical Discourse (EPD). This change in pedagogical discourse involves commognitive conflicts between the DPD and EPD. Data for the study include 8 videotaped sessions from a 2-year TEAMS PD for middle school mathematics teachers. Results show that conflict revolved around four themes. The most common was about students' abilities and its relation to instruction. The others were: Who is responsible for constructing mathematics knowledge in class? Limited view of the EPD, and what is considered ordinary instruction? We also identified four levels of conflict, ranging from commognitive conflict that is implicit to the participants, to conflict that is made explicit and reflected upon. Finally, results show movement from implicit conflict towards explication of conflict during the two years of the PD.