Resum: Engagement in risky behaviors is traditionally more prevalent among males than females, and the gap increases as youths move from adolescence to adulthood. Using the National Longitudinal Study of Adolescent to Adult Health, we identify a causal effect of exposure to high-school grade-mates with mothers who think that important skills for both boys and girls to possess are traditionally masculine ones (such as to think for oneself or work hard) as opposed to traditionally feminine ones (namely, to be well-behaved, popular, or help others) on the gender gap in teenagers’ engagement in risky behaviors. We find that a higher proportion of grade-mates’ mothers with non-traditional or non-stereotypical gender views who believe that independent thinking and working hard matter for either gender is associated with a reduction of the gender gap in risky behaviors both in the short and medium run. These results are driven by males curbing risky behaviors, suggesting that the relaxation of gender stereotypes results in boys behaving “more like girls”. In the long run, being exposed to grade-mates whose mothers have non-stereotypical gender beliefs reduces the gender gap in labor market outcomes by improving women’s performance. This evidence, together with our exploration of several potential mechanisms, suggests that the transmission of gender norms is driving our results.