Background: While socioeconomic status (SES) indicators such as parental educational attainment show robust associations with health behaviors such as substance use, the protective effects of these indicators may differ across racial groups. This phenomenon of weaker associations between SES indicators and health outcomes for marginalized and minoritized groups relative to non-Hispanic White people has been labeled “Marginalization-related Diminished Returns” (MDRs). Here, we test both whether parental educational attainment is associated with marijuana use frequency in youth as well as whether we observe racial and ethnic variation in this association consistent with MDRs. Methods: This study used data from the cross-sectional 2019 Monitoring the Future survey (MTF 2019). Participants included 29,230 youth who were either Hispanic (24.1%), non-Hispanic Black (16.1%), or non-Hispanic White (59.9%). We used weighted logistic regression models to test for (1) associations between maternal educational attainment and youth cannabis use frequency as well as (2) moderation of this association by race/ethnicity, while adjusting for the complex sample design of the MTF 2019 data. Age, sex, father presence, and maternal employment were entered into models as covariates. Results: Overall, children born to mothers with higher educational attainment reported less frequent marijuana use than peers born to mothers with lower educational attainment. However, this association was significantly weaker in Hispanic versus non-Hispanic White youth. Conclusion: The strength of the association between parental educational attainment and youth marijuana use frequency appears to differ across ethnic groups. Specifically, we observed that whereas non-Hispanic White youth from high-SES families tend to report less marijuana use than peers from lower-SES families, Hispanic youth report roughly equal levels of use across the full SES spectrum. This finding is in line with the MDRs framework and may reflect factors such as structural racism, social stratification, and the marginalization of ethnic minority families in the US.