The current study was designed to examine one possible weight stigma-reduction mechanism: school-level weight diversity. It was hypothesized that greater weight diversity among same-sex peers at school would attenuate the negative association between weight and academic achievement. Across 26 urban public middle schools, 5,991 sixth-grade students (52% girls) were included: 12% African American/Black, 14% East/Southeast Asian, 30% Latino, 21% White, and 23% from other specific ethnic groups. Weight diversity was estimated as the likelihood that two randomly selected students would be from different weight categories, using Simpson's index. Standardized achievement test scores and grade point average (GPA) were used to assess academic achievement. Consistent with our contextual moderator hypothesis, high levels of weight diversity at school served a protective function. The negative association between body mass index (BMI) and achievement test scores, as well as GPA (girls only) was nonsignificant at schools with high levels of weight diversity. The study results offer a potential explanation for inconsistent findings regarding body weight and achievement, and a novel methodological approach to capture weight diversity in ways that provide new insights for school-based interventions. Impact and Implications: The study results suggest that while overweight may be an academic risk factor in schools with little weight heterogeneity among students, weight-based achievement disparities appear to be minimized in middle schools with greater exposure to diverse body shapes and sizes.