In this project, we study the gender peer effects on students’ academic performance and non-cognitive outcomes. The analysis uses a nationally representative survey of middle school students in China and focuses on schools that randomly assign students to classrooms. Preliminary findings show that having a higher proportion of female peers in class improves students’ test scores and non-cognitive outcomes, such as mental stress, social acclimation and satisfaction, and disciplinary problems. There is evidence of improved classroom environment, teacher-student interactions, and teacher’s level of job satisfaction when there are more female students in the class.