Frustrated by his pupils' tendency to compartmentalise source analysis into two discrete parts of 'source' and 'own knowledge', Jonathan Sellin reflected that his use of scaffolds might be to blame. Inspired by recent work by teacher-researchers Hammond and King on the importance of secure substantive knowledge in the area of extended writing, Sellin theorised what might happen if he began with building pupils' contextual knowledge to answer a source question about usefulness before unveiling the source itself. In this article, Sellin explores how, by placing substantive knowledge first and foremost, pupils can be prevented from 'springboarding' in one direction from source into 'own knowledge', and instead begin to 'bounce' between them, allowing one to serve the other.