We examined whether African American students differentially responded to dimensions of the observed classroom-learning environment compared with non–African American students. Further, we examined whether these dimensions of the classroom mediated treatment effects of a preschool mathematics intervention targeted at students from low-income families. Three observed dimensions of the classroom (teacher expectations and developmental appropriateness; teacher confidence and enthusiasm; and support for mathematical discourse) were evaluated in a sample of 1,238 preschool students in 101 classrooms. Using multigroup multilevel mediation where African American students were compared with non–African American students, we found that teachers in the intervention condition had higher ratings on the observed dimensions of the classroom compared with teachers in the control condition. Further, ratings on teacher expectations and developmental appropriateness had larger associations with the achievement of African American students than for non–African Americans. Findings suggest that students within the same classroom may react differently to that learning environment and that classroom learning environments could be structured in ways that are beneficial for students who need the most support.