This article discusses the way teachers in primary and secondary schools in England engaged with a project to develop a Worldviews approach to Islam in the RE classroom. The project identified challenges and barriers to the teaching of Worldviews that were demonstrated by some teachers' unwillingness to engage with knowledge and curriculum content that they believed to be illegitimate or controversial. The authors use Basil Bernstein's idea of educational knowledge to explore the way teachers made decisions about what pupils should be permitted to learn about and what should be ignored in relation to Islam.