The effects of an antibullying program, KiVa, on Grade 1-3 teachers' perceptions of bullying were investigated. Data were gathered from 128 teachers in 33 intervention schools and 110 teachers in 29 control schools. Two-level regression models showed that, at the end of the intervention year, self-evaluated competence to tackle bullying was at a higher level in the intervention schools than in the control schools. In addition, in the intervention schools, participation in KiVa activities was associated with teacher perceptions of bullying. The need to take teacher and organization perspectives into consideration in future whole-school intervention studies is discussed. (Contains 5 tables.)