How do race and gender stereotypes affect public support for the punishment of Black girls? Across the USA, Black girls are suspended, expelled, arrested, and detained by educational and criminal justice institutions at disproportionate rates. Despite this, there is little research in political science investigating what drives this phenomenon. This paper uses original survey experimental data to examine how stereotypical public perceptions of Black girls shape support for their punishment and punitive policy more generally. We join previous research in finding race- and gender-based stereotypes intersect to produce a distinctive set of public perceptions rooted in the “adultification” of Black girls. In general, Black girls are seen as acting older than their age, more dangerous to others, and more experienced with sex than their peers. But, in an important extension, we also link these adultification stereotypes to support for harsher punishments for Black girls than for their peers and to support for punitive school policies more generally. Together, these findings point to the importance of understanding the intersectional nature of racialized and gendered public attitudes and help to draw the empirical link between the adultification of Black girls and support for their disproportionate punishment among the American public.