Research on school bullying and violence has always been working with taxonomies of bullying to categorize aggressive acts. Researchers distinguish between direct and indirect or between physical, verbal, and relational bullying. Cyberbullying is categorized either by type of action or by type of medium. In this article, we propose another kind of categorization: the taxonomy of reasons. A questionnaire was developed that asks for the five dimensions "instrumental," "power," "sadism," "ideology," and "revenge." It was tested with middle-school children in Germany. While bullies claim that their reasons were mostly revenge, victims mostly insinuate sadism and power. Both groups claim that ideology and instrumental violence play a little role. Confirmatory Factor Analyses (CFA) show that at least four of the theoretically proposed dimensions make sense (except instrumentality). A qualitative analysis of open answers shows that for future questionnaires, the taxonomy should include additional dimensions, such as peer pressure and lack of self-control.