Considerable research concerning determinants of teacher efficacy focuses on teachers' individual characteristics. School characteristics, such as the socioeconomic and gender composition of the school, are largely overlooked. The scant research including schools' student composition suggests that teachers feel less efficacious when teaching boys with a low socioeconomic status (SES). A multilevel analysis, using data from 1247 teachers in 59 Flemish secondary schools, shows that teachers' feelings of efficacy do not appear to differ very much between schools, although many studies assumed that the greater part of variance in teacher efficacy could be found between schools. The socioeconomic composition of the school does not affect teacher efficacy. Gender composition, however, does influence teacher efficacy, as teachers display more efficacy in classroom management and experience more general efficacy when teaching mostly boys. The unexpected finding that teachers seem to feel more efficacious in classroom management when teaching mostly boys is discussed.