We study the evolution of gender differences in the willingness to assume the decision-maker role in a group, which is a major component of leadership. Using data from a large-scale field experiment, we show that while there is no gender difference in the willingness to make risky decisions on behalf of a group in a sample of children, a large gap emerges in a sample of adolescents. In particular, the proportion of girls who exhibit leadership willingness drops by 39% going from childhood to adolescence. We explore the possible causes of this drop and find that a significant part of it can be explained by a dramatic decline in "social confidence," measured by the willingness to perform a real effort task in public. We show that it is possible to capture the observed link between public performance and leadership by estimating a structural model that incorporates costs related to social concerns. These findings are important in addressing the lower propensity of females to self-select into high-level positions, which are typically subject to greater public scrutiny.