The large number of newly arrived people from other countries, particularly children and youth, represents a major challenge for schools and school systems in the EU-28. The present study, conducted in Germany, investigated this situation using the critical incident technique. Critical incidents were collected in group discussions with teachers and principals about challenging events in the context of growing migration. The incidents, including their perceived causes and consequences, were categorised using qualitative content analysis. Events that were frequently present in teachers' everyday work included various types of conflicts concerning pupils, difficult cooperation between teachers and parents and parents banning their children from taking part in particular school activities. The identified causes for such events were diverse, including misunderstandings, diverging cultural and religious concepts, language barriers, structural constraints and some pupils' traumatic experiences influencing the school community. The described incidents had far-reaching consequences, especially for parent-school cooperation and for pupils' integration in the classroom community and academic and personal development. The final part of this article discusses and illustrates how the results can contribute to developing ideas and measures to deal with the identified challenges.