Gender differences in reading and math have been reported for many years. Girls outperform boys in reading (representing a school domain stereotyped as female); boys often perform slightly better in math (a stereotypical male domain). Research has so far investigated the contribution of domain-specific academic self-concepts and interests as well as gender stereotypes to these gender differences. Students' gender role attitudes (GRAs) and their relation with gender disparities in school performance, however, have been studied little. This study examines if students' GRAs contribute to explaining boys' higher math achievement and girls' higher reading achievement. Using PISA-2009 data from Germany, the sample included 9,460 grade nine students (49.70% girls; M[subscript age] = 15.61 years). Regression analyses revealed that egalitarian GRAs are beneficial for all students. Still more so for girls, egalitarian GRAs help girls perform particularly well in reading and compensate for possible disadvantages in math. In reading, girls with egalitarian GRAs reached higher performance scores than boys with egalitarian GRAs. In math, girls with egalitarian GRAs scored nearly as high as boys with egalitarian GRAs. Boys also benefited from egalitarian GRAs, although not as much as girls. Although gender disparities in reading and math achievement were explained only partly by students' GRAs, supporting boys and girls in endorsing egalitarian GRAs is worthwhile as they may help to increase societal gender equality more broadly.