The tendency to make hostile attributions in ambiguous social situations has been associated with aggression and may be targeted through cognitive bias modification for interpretations (CBM-I). Despite their high prevalence of aggression and internalising problems, children and young people with neurodevelopmental disorders (NDD) or special educational needs (SEN) are markedly absent from CBM-I studies. This pilot study investigates whether online CBM-I can reduce hostile attributions and reactive aggression in inclusive school pupils. In Study 1, 71 pupils (mean age = 12.2, SD = 1.5; 25.4% presented with NDD or SEN) were randomly allocated to complete three sessions of either CBM-I (n = 37) or active control training (n = 34). CBM-I involved interpreting ambiguous scenarios or faces in a non-hostile manner, whereas the control training involved attention and memory exercises without resolving ambiguity. Between-group comparison showed CBM-I to reduce both hostile attributions and reactive aggression. In Study 2, follow-up focus groups with 23 pupils demonstrated the acceptability of training content and delivery. Together, these findings show online CBM-I to be acceptable and effective at reducing both hostile attributions and reactive aggression in an inclusive setting. The possibility of intervention effects on behavioural outcomes and potential confounding variables require further investigation.