Despite progress in recent years, girls and women remain disadvantaged relative to boys in many parts of the world, with multiple negative potential implications. At the heart of gender inequality are social norms and attitudes about gender that give rise to and perpetuate discriminatory institutions, and ultimately inhibit institutional and behavioral change. Despite this, little is understood about the how gender norms and attitudes evolve and adapt. One important question is why is gender inequality acute and persistent in particular societies but not others? A related question is how readily do gender attitudes evolve when women are given more opportunities to advance and thereby influence perceptions about women's relative ability? This project will contribute to our understanding of both questions by collecting new and unique data that will be used to investigate how gender attitudes respond to improvements in girls' schooling and a narrowing of the gender gap in cognitive ability that arose from reductions in fetal iodine deficiency in Tanzania. In particular, data from a previous evaluation of the Tanzania maternal iodine supplementation program showed that girls born during the program had achieved nearly a year of additional schooling attainment by ages 12-15, whereas boys benefited very little, consistent with scientific evidence that iodine deficiency is more acute for females at early stages of brain development. The study will track 1200 households from 16 districts of Tanzania that benefited from the program and collect data on gender attitudes of parents of children born during the program using Implicit Association Tests (IATs), and data on economic outcomes of their children. The study aims to: (1) Develop culturally appropriate IATs to measure gender attitudes and stereotyping, and dewvelop and test survey questions to measure explicit beliefs about male and female relative ability and gender stereotyping; (2) Assess the causal effect of reductions in fetal iodine deficiency among girls on parental gender attitudes by making use of quasi-experimental variation in program exposure that has been established in previous research in conjunction with the data we collect from parents on gender attitudes and preferences; and (3) Assess the feasibility of conducting a survey of children who benefited from in utero supplementation by collecting location information and gathering proxy data on kids' long-run outcomes. The proposed study will be the first to use rigorous, recently developed approaches to assess the causal association between girls' susceptibility to fetal iodine deficiency and parental gender attitudes.