Sixty elementary-school children (9–10 years old) and 82 adolescents (12–13 years old) completed explicit and implicit measures of racial stereotypes about math. 60 Asian, 42 Latino, 21 White, 15 Black, and four multiracial students participated (42% boys). On the explicit measure, children as early as fifth grade reported being aware of the stereotype that Asians = math, but only adolescents personally endorsed this stereotype. On the implicit measure, there was significant evidence for racial stereotypes about math among adolescents. Across both ages, individual students' explicit awareness of the stereotype was significantly correlated with their implicit stereotypes. Early adolescence is a key developmental window for discussing stereotypes before they become endorsed as personal beliefs.