Schools' sex composition and gender role attitudes are often overlooked in teachers' self-efficacy studies, while research suggests that gender role attitudes may color teachers' perceptions of students. This study investigates the association of schools' sex composition and teachers' gender role attitudes with teachers' self-efficacy in instructional strategies, classroom management and student engagement, and how this latter association might differ between schools with more boys or girls. A multilevel analysis was carried out on data of 1247 teachers in 59 schools (2012-2013). Teachers feel more efficacious in classroom management in schools with more boys, especially male teachers with traditional gender role attitudes. Male teachers with traditional gender role attitudes feel less efficacious in classroom management in mixed schools. Female teachers feel less efficacious in all dimensions when holding traditional gender role attitudes, regardless of schools' sex composition. The results highlight the importance of addressing gender bias in teacher training in order to improve teachers' self-efficacy across all dimensions.