Even though teachers are key figures of a program's effectiveness, most intervention studies have not focused explicitly on the effects of antibullying programs at teacher level. We conducted a meta-analysis into the effects of school-based antibullying programs on determinants of teacher intervention, including teachers' attitudes towards bullying, their self-efficacy and knowledge regarding intervention strategies, and the effects on teachers' bullying intervention itself. Following the PRISMA guidelines, 13 peer-reviewed papers were retrieved that reported outcomes on teachers, staff, and students (N = 948, 2,471, and 138,311, respectively). Antibullying programs had a significant moderate effect on determinants of teacher intervention (g = 0.531) and a significant small to moderate effect on teacher intervention in bullying situations (g = 0.390). Results of the meta-analysis indicate that the effectiveness of antibullying programs may increase when components are included to reinforce teachers' attitudes, subjective norms, self-efficacy, knowledge, and skills towards reducing bullying in the school.