At secondary schools at the latest, there is at least one class chat in almost every class, often even several in parallel. However, in addition to organizational information and agreements, harmful and forbidden content is also shared in unregulated class chats or cyberbullying takes place. In order to prevent such problems and excessive demands due to message spam, rules for the group chat should be defined together with the pupils at the beginning of the school year. Our class chat teaching unit, which we have updated and expanded to include new case studies, is suitable for this purpose.