While teaching, teachers need to access both their knowledge of mathematics and knowledge of pedagogy. Practice-based materials afford teachers opportunities to reason about both mathematics and pedagogy within the context of teaching. Accepted systems exist for explaining and reasoning in the domain of mathematics; logic, procedures, and representations all serve as instances of mathematics that bear common meaning in the domain. In contrast, there is not an accepted well-structured system for reasoning within the domain of pedagogy; rather, it is an inherently interpretive act. This paper explores differences in knowledge bases and reasoning by examining discourse about mathematics and pedagogy in a practice-based teacher education course. Mathematics conversations featured greater depth of conversation, more challenges, and more echoes of previous claims. Pedagogical conversations were denser and featured more qualified statements and more evidence from personal values or opinions. Implications for the design of teacher education and professional development experiences are presented.