Peer gender and mental health

Adolescent mental health is key for later well-being. Yet, causal evidence on environmental drivers of adolescent mental health is scant. We study how an important classroom feature-the gender composition in compulsory-school-affects mental health. We use Swedish administrative data ( N = 576 , 285) to link variation in gender composition across classrooms within cohorts to mental health. We find that a higher share of female peers in a classroom increases the incidence of mental health diagnoses, particularly among boys. The effect persists into adulthood. Peer composition is thus an important and persistent driver of mental health.(c) 2022 The Author(s). Published by Elsevier B.V.This is an open access article under the CC BY license( http://creativecommons.org/licenses/by/4.0/ )