Societal norms about gender roles contribute to the economic disadvantages facing women in many developing countries. This paper evaluates an intervention aimed at eroding support for restrictive gender norms, specifically a multi-year school-based intervention in Haryana, India, that engaged adolescents in classroom discussions about gender equality. Using a randomized controlled trial, we find that the intervention increased adolescents' support for gender equality by 0.25 standard deviations, a sizable effect compared to other correlates of their gender attitudes such as their parents' views. Program participants also report more gender-equitable behavior; for example, boys report helping out more with household chores.