To examine whether high moral reasoning competence of adolescents is associated with low levels of bullying, and to understand whether moral disengagement mediates or moderates this relationship, 925 German children ranging from 11 to 17 years of age (M = 14.18, SD = 1.21) completed questionnaires on moral reasoning competence and moral disengagement in surveys at three different schools. The children were classified according to their bullying role, based on a peer‐nomination procedure. Multinomial logistic regression analyses showed that moral reasoning competence negatively predicted whether a student took an aggressive role. Moral disengagement partially mediated this relationship. Corresponding effects for defenders and outsiders were not found. These results extend previous findings about the effect of moral reasoning on bullying in primary school. The implications for the prevention of bullying are discussed.