Are there things schools can do to build pupils’ resilience to extremism? The UK ‘Prevent duty’ assumes there are, but schools are poorly served by existing government advice. Here I offer a cautious defence of the idea that the acquisition of extremist beliefs and attitudes can be forestalled by educational means. I begin by sketching, and modifying, Quassim Cassam’s family resemblance account of the concept of extremism. I then focus in on what I take to be a core ideological commitment of extremism: the belief that there is an ideal so worthy as to exempt those who pursue it from the requirements of basic morality. I argue, first, that it is permissible for educators to forestall the exemption-from-basic-morality belief and, second, that it is possible for them to do so.