Increased exposure to gender-role information affects a girl's educational performance. Utilizing the classroom randomization in Chinese middle schools, we find that the increased presence of stay-at-home peer mothers significantly reduces a girl's performance in mathematics. This exposure also cultivates gendered attitudes towards mathematics and STEM professions. The influence of peer mothers increases with network density and when the girl has a distant relationship with her parents. As falsification tests against unobserved confounding factors, we find that the exposure to stay-at-home peer mothers does not affect boys' performance, nor do we find that stay-at-home peer fathers affect girls' outcomes.