This article reports on the differential impact of a curriculum intervention on students' understanding and practice of virtue. The research is germane given Ofsted's new requirement that its inspectors should assess how the curriculum in all schools in England and Wales supports students' character development. Results are reported here for a total of 1226 eleven- and twelve-year-olds assessed at the beginning and end of their first secondary school term: 822 children in nine program schools, where students experienced the "Narnian Virtues" character education English curriculum, and 404 children in eight control schools that did not experience the intervention (2 lessons per week over 12 weeks). Mean scores for knowledge and understanding of virtues (wisdom, love, integrity, fortitude, self-control and justice) in the experimental group showed a significant increase from pre- to post-test, which was not the case for the control group. Although scores pre- to post-test for the experimental group declined on a number of (self-assessed) character measures, this decline was not as pronounced as it was for the control group. That children's understanding of character improved rapidly in the experimental group is important, as knowledge of virtue generally precedes behavioural application.