This paper studies the interplay between major returns, preferences, and market design in explaining the gender earnings gap. Information on preferences allows us to estimate the major impacts while accounting for selection on rich sources of preference heterogeneity. We use this to estimate pecuniary and non-pecuniary returns to majors. We find substantial heterogeneity in earnings and fertility impacts, with sizable gender differences in each. We find that pecuniary returns are most predictive of male gender choices and the opposite is true for females, providing evidence about an important pre-labor market choice that causes a rift in the educational decisions of men and women. The interaction of gender, major choice, earnings, and fertility are captured by the substantial heterogeneity in child penalty gaps across fields of study, ranging from no short-run penalty to as high as 43%. Motivated by the fact that preferences are hard to change and that most of the gap is due to differences in representation, we fix preferences and consider policy-relevant counterfactuals leveraging the transparent rules embedded in a centralized assignment system. Our results suggest that slight gender-specific quotas can substantially reduce the gender earning gap among college graduates with essentially no impact on aggregate efficiency.