In this paper, we frame mathematics classrooms as heterogeneous spaces wherein students draw on multiple storylines based on different notions of schooling and school mathematics to both communicate mathematical ideas and position themselves and one another. We focus on a fourth grade (age range 9.4-10.8 years) mathematics classroom discussion in a racially and linguistically diverse urban school in the Southeastern US. Our results reveal that some students drew from traditional notions of school mathematics focused on evaluating right and wrong answers, while others drew on a more dialogic notion of school mathematics supported by local ground rules for making reasoning explicit, revising one's thinking, and inviting multiple voices. The result was a heterogeneous space that both enabled and constrained possibilities for the construction of a dialogic space. We end with a discussion of the complexities of dialogic teaching in mathematics classrooms given the discipline's narrative history.