Robin Conway suspected that his students’ concepts of the significance of different aspects of historical periods was affected by the preconceptions that they brought to his lessons. These preconceptions were leading his students into making unhistorical judgments, without any real understanding on their part of what had affected their thinking. He has designed, and here recounts, an experiment to consider the extent to which his students have been affected. He also suggests a scheme of categorisation for the preconceptions students bring to history, and puts forward some tentative ways in which pupils’ preconceptions might be challenged, leading them into making increasingly historical judgments.