Ethnic-racial discrimination is a pernicious experience that affects discriminated adolescents' healthy human development, but the spillover consequences of discrimination on the nondiscriminated adolescent population are less clear. Adolescents who vicariously witness their classmates experience ethnic-racial discrimination from educators may question their educators' authority and classroom rules, and educators who perpetuate discrimination may engage in other practices that disadvantage the entire classroom. Thus, we posed three research questions: Did classmates' ethnic-racial discrimination from teachers predict adolescents' classroom adjustment outcomes (e.g., class grades, test scores, and engagement), did classroom climate mediate the link between classmates' ethnic-racial discrimination and adolescents' classroom adjustment outcomes, and did the results differ between early versus middle adolescents? To answer these research questions, the present study leveraged longitudinal data among 1,539 adolescents (Mage = 13.81, SDage = 1.49; 60% Black, 30% White, 9% other, 1% Asian; 49% female, 51% male) nested in 104 math classrooms, as math is a subject domain with pervasive ethnic-racial stereotypes about students' abilities and opportunities to succeed in class. Results illustrated that direct and vicarious ethnic-racial discrimination from math educators in the fall semester predicted worse math course grades, state-administered standardized test scores, and classroom engagement across the fall and spring semesters. Math classroom climate perceptions mediated the longitudinal relations between ethnic-racial discrimination and their math adjustment outcomes, and the role of ethnic-racial discrimination varied across different developmental stages of adolescence. Implications for the measurement of ethnic-racial discrimination in the classroom context and the social contagion linked to ethnic-racial disadvantage are discussed. (PsycInfo Database Record (c) 2024 APA, all rights reserved).