Article dans une revue: In most developed countries, students have to choose a major field of study during high school. This is an important decision as it largely determines subsequent educational and occupational choices. Using French data, this paper reveals that enrollment at a more selective high school, with higher-achieving peers, has no impact on boys, but a strong impact on girls’ choices: they turn away from scientific fields and settle for less competitive ones. Our results are not consistent with two commonly-advanced explanations for gender differences in field of study, namely disparities in prior academic preparation and in sensitivity to rank in class.