This study examined the effects of racial/ethnic segregation (i.e., overrepresentation) in academic classes on belonging, fairness, intergroup attitudes, and achievement across middle school (n = 4,361; M[subscript age T1] = 11.33 years), and whether effects depended on numerical minority status in school and race/ethnicity. Latent growth curve models revealed that experiencing more segregation "than usual" predicted less belonging and fairness "than usual" for all youth in the numerical minority, and greater in-group preference for numerical minority Whites. Academic classroom segregation throughout middle school predicted less steep declines in in-group preference for adolescents in the numerical minority, and declines in achievement for African American numerical minority youth. Results highlight the need to treat the racial/ethnic context as a structural and dynamic construct.