In 2010, the Ministry of Education in Trinidad and Tobago converted 20 low-performing secondary schools from coeducational to single-sex. I exploit these conversions to identify the policy-relevant causal effect of introducing single-sex education into existing schools (holding other school inputs constant).
After accounting for student selection, boys in single-sex cohorts at conversion schools score higher on national exams taken around age 15, both boys and girls take more advanced coursework, and girls perform better on secondary-school completion exams. There are also important non-academic effects; all-boys cohorts have fewer arrests as teens, and all-girls cohorts have lower teen pregnancy rates. Survey evidence suggests that these single-sex conversion effects reflect both direct gender peer effects due to interactions between classmates, and indirect effects generated through changes in teacher behavior.