Past research extensively documents inequalities in educational opportunity and achievement by students' race/ethnicity or socioeconomic status (SES). Less scholarship focuses on how race/ethnicity and SES interact and jointly contribute to educational inequalities. We advance this burgeoning line of scholarship by charting math achievement trajectories and school socioeconomic composition by both student race/ethnicity and SES in California from 2014-15 through 2017-18. Linked administrative data allow us to operationalize student SES more richly than point-in-time free meal eligibility, a measure commonly used in education research. We find evidence of considerable racial/ethnic disparities in math achievement and school socioeconomic composition among same-SES students. White and Asian students score substantially higher on math achievement tests and attend higher-SES schools than same-SES Hispanic and Black students. Achievement and contextual inequalities are related: differential exposure to school SES by student race/ethnicity is associated with within-SES racial/ethnic achievement disparities. Our findings show that SES does not translate into the same contextual or achievement advantages for students of all racial/ethnic groups, demonstrating the importance of jointly considering student race/ethnicity and SES in future research and policy development.