The political drive for inclusion means there are increasing numbers of children with autism spectrum disorder (ASD) being educated alongside their neurotypical peers. Pervasive victimisation has prompted the development of peer interventions targeting stigma. This study evaluated the ‘Understanding Our Peers with Pablo’ programme for effects on knowledge, attitudes and behavioural intentions of infant schoolchildren (N = 222) towards autistic peers. Classes were randomly assigned to an intervention or waitlist control condition. Change over time in knowledge of autism and attitudes and behavioural intentions towards familiar and unfamiliar peers was analysed using mixed analyses of variance. The intervention condition showed gains in knowledge and increased positive attitudes towards unfamiliar autistic peers (maintained over three-months). There were significant improvements in attitudes towards familiar autistic peers, and time-limited decreases in behavioural intentions across both conditions. Overall, results support the use of this programme in early-years education.