In advanced economies, growing population diversity often fuels hostility toward immigrants and deepens social divides. We study a short educational program for high-school students designed to promote cultural diversity and improve attitudes toward immi- gration through active learning. Using a randomized controlled trial involving 4,500 students from 252 classes across 40 schools in northern Italy, we find that the program fostered more positive attitudes and behaviors toward immigrants, particularly in more diverse classrooms. In terms of mechanisms, the intervention reduced students’ misperceptions and shifted perceived classroom norms, but did not affect implicit bias, empathy, or social networks. Our findings indicate that anti-immigration attitudes largely stem from stereotypes and broad societal concerns, and that educational pro- grams combining factual learning with norm-shaping elements, such as critical thinking and structured intergroup engagement, can effectively mitigate them.