Student perceptions are a pivotal point of measurement for understanding why classroom learning environments are effective. Yet there is some evidence that student perceptions cannot be reliably aggregated at the classroom level and, instead, could represent idiosyncratic experiences of students. The present study examines whether heterogeneity in student perceptions of the classroom climate has implications for student achievement. We use data from 1428 seventh grade students in 75 mathematics classrooms from the Michigan Study of Adolescent and Life Transitions. Three dimensions of student perceptions of the classroom were measured: emotional support, autonomy support and performance focus. To obtain a measure of heterogeneity, we first reduced the data using latent profile analysis to describe profiles of students' perceptions of the classroom. Next, we quantified the heterogeneity of student perceptions within classrooms using Simpson's D. Classroom-level heterogeneity (Simpson's D) of students' perceptions was negatively associated with students' mathematics achievement, even after controlling for individual- and classroom-level previous achievement, student's prior perceptions and other variables. Findings suggest that measures of heterogeneity in student perceptions might be important for understanding classroom- and teacher-level effects on student outcomes.