Focusing on students' attempts to explain the relative significance of different factors in Hitler's rise to power, Catherine McCrory explores the vexed question of why students who seem able to express necessary historical knowledge on one occasion cannot effectively reproduce it on another. Drawing on a detailed analysis of what it actually means to "know" something, she plans a series of accessible activities allowing as many students as possible to secure essential knowledge for themselves, rather than simply relying on the authority of the teacher who told them. She goes on to explain how careful diagnosis of the gaps between what students say and the reasoning that underpins their utterances can help teachers to decide where they can usefully "give" students particular insights and where the students need to "arrive at" those insights through their own cognitive labour.