The project „Promoting Friendships in Heterogeneous Classrooms“ aims to enable the social participation of children with special educational needs (SEN). It is based on the latest scientific evidence, showing that friendships between children with and without SEN are a key element in building social skills and protecting children with SEN from being socially excluded. The project is based on a children's detective book written especially for the project by Jeanine Grütter and children's book author Katja Alves. The story, which is read to the students in six sections, offers a model for friendships between very different children and takes up central themes such as dealing with being different, the choice of friends, the quality of friendship, dealing with conflicts, and civil courage. The content of the story is then deepened through discussions and exercises. An instruction manual and teacher-trainings prepare teachers for program implementation and provide them with important scientific theories for personal familiarization with the topics and reflection on their attitudes toward being different. Overall, the program is suitable for grades 3 to 6 and provides material for six double lessons. The effectiveness of the program is currently tested through a randomized experimental design.