The knowledge structures and reasoning processes that underlie the use of external representations (ERs) in individuals with autism spectrum disorder (ASD) are not well understood. We compare the organisation of knowledge of ERs in young people with ASD, with an age-matched typically developing control group. Participants were given an ER card-sorting task. The ERs were based on representations used in educational software, and included graphs, charts and text. Cluster analysis of the card-sorts revealed broadly similar clusters for both groups. However, there was a difference in ‘basic level’ categories. While in the non-ASD group, maps were the most distinctive category, analysis of the ASD cluster revealed, in addition, another ‘basic level’ category of text. These results are discussed in relation to theories of information processing in autism, and we draw implications for educational software in which ERs are able to support differences in information processing for individuals with ASD.