In considering "good teaching" in mathematics, scholars usually refer to teacher knowledge and instructional practices that promote understanding. However, researchers have found that these two elements of instruction are often not as prevalent in urban contexts, a space where high percentages of students of color and the poor are educated. Additionally, recent work calls for understanding other classroom mechanisms that impact the mathematics learning of students of color. Using video, field notes, and an interview, this research examines a case study of one urban classroom of Latino and African American students. Their teacher engages them in substantive mathematics and reform-minded pedagogical strategies, but a number of relational interactions raise issues of how these micro-interactions can mediate access to mathematics. The study found four dimensions in which relational interactions mediated access to mathematics: addressing behavior, framing mathematics ability, acknowledging student contributions, and attending to culture and language. The paper ends with raising questions for future research and calling for a broader framing of instruction that incorporates relational dimensions of the classroom.