Background/Context: Brown v Board of Education fundamentally changed our nation's schools, yet we know surprisingly little about how and whether they provide equality of educational opportunity. Although substantial evidence suggests that African American and Latino students who attend these schools face fewer learning opportunities than their White counterparts, until now, it has been impossible to examine this using a representative sample because of lack of data. Purpose/Objective/Research Question/Focus of Study: This study uses newly available data to investigate whether racially diverse high schools offer equality of educational opportunity to students from different racial and ethnic groups. This is examined by measuring the relative representation of minority students in advanced math classes at the beginning of high school and estimating whether and how this opportunity structure limits the level of achievement attained by African American and Latino students by the end of high school. Setting: This study uses data from the Adolescent Health and Academic Achievement Study (AHAA) and its partner study, the National Longitudinal Study of Adolescent Health (Add Health), a stratified, nationally representative study of students in U.S. high schools first surveyed in 1994-1995. Population/Participants/Subjects: Two samples of racially diverse high schools were used in the analysis: one with African Americans, Whites, and Asians (26 schools with 3,149 students), and the other with Latinos, Whites, and Asians (22 schools with 2,775 students). Research Design: Quantitative analyses first assess how high schools vary in the extent to which minority students are underrepresented in advanced sophomore math classes. Hierarchical multilevel modeling is then used to estimate whether racial-ethnic differences in representation in advanced math have an impact on African American and Latino students' achievement by the end of high school, relative to the Whites and Asians in the school. Specifically, we estimate the effects of Whites' and Asians' overrepresentation in sophomore-year math (or Latino or African American underrepresentation) within the school on students' senior-year grades and their postsecondary enrollment. Findings/Results: Findings show that schools vary in the extent to which African American and Latino students are underrepresented in advanced sophomore math classes. This pattern of racial inequality in schools is associated with lower minority senior-year grades and enrollment in 4-year postsecondary institutions, net of students' own background. Conclusions/Recommendations. Evidence consistently suggests that schools can play an active role in the provision of opportunities for social mobility or in the exacerbation of social inequality, depending on how they are structured. It is important to consider racial stratification within schools as a mechanism of inequality of educational opportunity.