Girls presently outperform boys in overall academic success. Corresponding gender stereotypes portray male students as lazy and troublesome and female students as diligent and compliant. The present study investigated whether these stereotypes impact teachers' perceptions of students and whether students' visible enactment of their gender at school (behaving in a very masculine or feminine way) increases the impact of these stereotypes on teachers' perceptions of students. We hypothesized that teachers would ascribe more behavior that impedes learning and less behavior that fosters learning to male students who enact masculinity as compared with male students who show gender-neutral behavior and female students. Three pilot studies (N = 104; N = 82; N = 86) yielded pretested material for a randomized vignette study of N = 104 teachers. The teachers read one randomly assigned vignette describing a male (or female) student enacting his (or her) gender (or not) and rated how likely this student would be to display behaviors that impede or foster learning in a 2 (between: target students' gender) × 2 (between: gender enactment [yes/no]) × 2 (between: teachers' gender) × 2 (within: ascribed behavior) factorial design. As expected, male students enacting masculinity were rated as showing the lowest amount of academic engagement. Results are discussed with regard to the current debate on the causes of boys' lower academic success.