This dissertation investigated the role of teachers and classmates in school bullying. The three main findings were:

1. Teachers may not be fully equipped to tackle bullying
This dissertation suggests that teachers affect the prevalence of bullying, but that they may not be fully equipped to tackle bullying. The investigated teachers did not exactly know what bullying is, used inefficient methods to detect bullying, and often did not perceive students who claimed to bullied as victims. Teachers may underestimate the complex nature of bullying: some teachers reported that they find it easy to stop bullying, whereas in fact many students in their classrooms were bullied.

2. Teachers and classmates do not recognize bullying
The second finding is that there are large discrepancies between victimization reports of students, their classmates, and their teachers. This is worrying, because it may imply that teachers and classmates do not know which students are bullied.

3. The classroom composition matters
Finally, this dissertation suggests that the classroom composition affects the bullying process. Fewer students were bullied in multi grade classrooms. It could be that due to the mix of older and younger students there is less competition in these classrooms. Moreover, students in larger classrooms seemed to less often recognize bullying. A possible explanation for this finding is that students in large classrooms do not know each other well.