The teaching of computing, like all subjects, requires a range of strategies to take the curriculum content (skills, knowledge, understanding and attitudes) and put it in a form that is more easily learned by students. Metaphor has a particular role in the world of computing: embedded in the design of computer hardware and software; part of the human-computer interface and underpinning important facilities such as icons, pointer actions and window displays. It is proposed that metaphor plays a particular role in pedagogic content knowledge and the training of computing teachers. This article reports on the research undertaken to identify the role metaphor plays in the teaching of computing. Through discussion of a number of difficult-to-teach topics an analysis of pedagogic approaches is made. The theoretical background of metaphor is explored and used as the context for describing pedagogic content knowledge. The research adopts a grounded theory approach using text analysis software to record and process a range of documents, statements, textbook analyses and interview transcripts of experienced and successful computing teachers. The outcomes of the research reveal a new perspective upon pedagogic content knowledge with respect to the teaching of computing in post-compulsory education. A model of approaches that identifies the key areas and emphasises the role metaphor plays in both the teaching strategies and the subject knowledge of computing, is presented. (Contains 5 figures.)