Culturally diverse schools contribute to adolescents' intergroup relations. Complex and inclusive social identities are mechanisms that can explain the link between structural school cultural diversity (i.e., proportion of students of immigrant descent and the number of different ethnic groups) and positive intergroup relations. We expected that similar mechanisms might be at play linking cultural diversity approaches in schools with adolescents' intergroup relations. We examined the link between two sub-dimensions of cultural diversity approaches (i.e., equal treatment; heritage and intercultural learning) and adolescents' prosocial intentions and behaviour towards refugee youth. Then, we explored the mediating role of identity inclusiveness (i.e., perceived similarity of the self with others). We sampled culturally diverse eighth grade adolescents from 54 classrooms in Berlin (N = 503, Mage = 13.76 years, 50.6% female). Surveys measured perceived cultural diversity norms, adolescents' perceived identity inclusiveness with refugee youth, prosocial intentions to support refugee youth, and willingness to donate to a project for refugee youth. Multilevel models revealed that adolescents' perception of heritage and intercultural learning predicted adolescents' prosocial intentions towards refugee youth, but not their willingness to donate. Equal treatment was not a significant predictor of adolescents' prosocial intentions towards refugee youth, or their willingness to donate. Identity inclusiveness did not mediate the relation between cultural diversity approaches and prosocial intentions. However, identity inclusiveness did positively relate adolescents' prosocial intentions and willingness to donate. We conclude that culturally diverse schools that engage in heritage and intercultural learning might help to promote positive relations between local and refugee youth in schools and society. Fostering inclusive identities may enhance local adolescent's prosocial intention and behaviour.