Background/Context: Research shows that teachers' understandings of students, subject, and teaching influence their classroom practice. Additionally, teachers' colleagues have a role in shaping individuals' approaches to teaching and their responses to reform. Focus of Study: To understand how interactions with colleagues support teachers' informal learning, I examined teachers' collegial conversations in a highly collaborative teacher community. Setting: This research took place within a collaborative, improvement-oriented urban high school mathematics department that showed evidence of increasing access to and rigor in its curriculum. Participants: Six high school mathematics teachers and the researcher as a participant observer worked together in a group focusing on detracking ninth-grade algebra classes. Research Design: This 2-year ethnographic study went inside the teacher community, with the researcher teaching alongside the teachers to gain access to their interactions and workings. Data Collection and Analysis: Approximately 100 hours of teachers' collaborative conversations were observed and recorded through audio- and videotape and field notes. Using a situated learning framework and sociolinguistic analyses, I examined teacher-to-teacher talk that constituted episodes of pedagogical reasoning (EPRs) to understand how collegial conversations provide resources for teacher learning. Findings: Across EPRs, two forms of discourse were important sites for representing, and sometimes learning about, teaching practice, which I call teaching replays and teaching rehearsals. Extended replays or rehearsals supported a re-visioning routine, interactions in which teachers elaborated, reconsidered, or revised their understanding of complex teaching situations while providing particular, emotionally involving accounts of the classroom. The examination of these interactions further specifies conditions that support teachers' collegial learning. Conclusions: Theoretically, this article illustrates a process of learning as recontextualization, as the teachers work between general teaching principles and specific occurrences in their classrooms. Practically, by highlighting the work that teachers do to make sense of innovative practices, this analysis provides a description of how collegial conversations can support teachers' informal learning, supporting the development of professional communities.