The particular significance of peer groups in a child’s development and personality formation has been an important subject in developmental psychology, social psychology and sociological work for a long time. The peer group has proven to be a factor in socialisation whose effect is comparable to that of the family. Relationships with peers are an additional developmental resource; they constitute a ‘developmental support factor’ (Ahnert 2005, p. 349); peers are, in fact ‘developmental assistants’ (Seiffge-Krenke 2004, p. 121 ff). The peer group fulfils important functions in childhood development all the way up to adolescence: it provides children with the opportunity to live out and act out conflicts in the context of shared play. It allows them to test and practice new roles which—unlike those in the family—are not determined by age or gender, and to test the degree to which norms are binding or obligatory. By socialising them in terms of communication and cooperation, the peer group prompts children to move beyond self-centredness; it strengthens egalitarian aspects within the child through acknowledgment and rejection; it presents the child with the task of defining his or her relationship to these ‘others’. In a peer group situation, children have to express their needs, declare their intentions, and, in a process of mutual consent, agree upon norms, rules and sanctions—and perhaps change them once again.