Students who repeat a grade are at a higher risk of dropping out of high school. Previous research has examined this in a methodologically aggregated way (e.g., repeated any grade versus never repeated) or only specific grades/grade ranges (e.g., Kindergarten or elementary) leaving questions about which grades are more detrimental to repeat with respect to school dropout. This study uses data from the National Center for Education Statistics (N = 9,309) to comparatively examine which grades, when repeated, show the strongest associations with dropping out. Overall, those who repeated sixth or seventh had the highest odds of dropping out of high school with unique patterns by gender and race/ethnicity. These grades are typically when youth transition into middle school. When examined through a developmental lens, these results highlight the important impact that grade retention while youth experience other normative physical, cognitive, and social changes.