In American high schools female students put greater effort into school and outperform boys on indicators of academic success. Using data from the High School Longitudinal Study of 2009, we found female students' greater academic effort and achievement was partly explained by different social incentives to trying hard in school experienced by male and female students. Males were 1.75 times as likely to report they would be unpopular for trying hard in school and 1.50 times as likely to report they would be made fun of for trying hard in school. Social costs to trying hard in school were directly associated with less rigorous mathematics course-taking and indirectly associated with lower GPA in STEM courses through lower academic effort.