This study used the Theory of Planned Behaviour to explore the attitudes, behavioural intentions and behaviour of 318 mainstream primary school children in an urban East London borough towards peers with Autism Spectrum Disorders (ASD). Pupils were presented with a vignette about a hypothetical peer with ASD then completed self-report questionnaires and peer socio-metric measures. The results showed that children's attitudes, the social pressure they felt from others and the amount of control they felt they had over their own behaviour, significantly predicted their behavioural intentions to befriend a peer with ASD. The strongest association was between perceived behavioural control and behavioural intentions. A significant association was also found between children's behavioural intentions and actual behaviour towards an included peer. Support was therefore found for the use of the Theory of Planned Behaviour as a valuable tool by which to explore the social inclusion of children with ASD.