The role of racial stereotypes in youth’s academic achievement becomes salient during adolescence. Yet, very few studies have investigated whether associations between Black and White American adolescents’ stereotype endorsement and their cognitive engagement, mindset beliefs, and performance in math differed by stereotype valence (i.e., positive versus negative) and youth gender. To address these gaps, this 3-year longitudinal study (n = 2546; age range = 11-16; 50% males, 60% White, 40% Black; 57% qualified for free lunch) investigated (a) whether Black and White American adolescents’ endorsement of positive and negative racial stereotypes differentially related to their cognitive engagement, ability mindset, and math performance and (b) whether gender moderated these relations. The results revealed that endorsing either negative or positive racial stereotypes (as opposed to those with unbiased beliefs) was linked to lower cognitive engagement and stronger fixed mindsets in math 1 year after, while endorsing negative racial stereotypes was linked to lower math scores. In addition, the intersection of adolescents’ race and gender moderated some of the observed effects. The inverse link between negative stereotype endorsement and math cognitive engagement was significant for Black girls but not for Black boys. The positive link between negative stereotype endorsement and fixed math ability mindset was stronger for Black girls than Black boys, whereas the link was stronger for White boys than White girls. These findings shed light on the direction and strength of the links between racial stereotype valence and math outcomes among Black and White youth.