Research suggests that children with behavioural difficulties exhibit "positive illusory bias" (PIB), in which they overestimate their competencies leading to a perception of self that is more positive than the perceptions held by their peers, parents or teachers. However, research to date has focused on children of elementary school age and none has examined the potential role of oral language competence. This study investigates whether children aged 9-16 years with a history of disruptive behaviour exhibit PIB when compared to students with no such history, and whether there are differences between groups in expressive and receptive vocabulary. We found significant differences between groups in expressive vocabulary, but minimal differences between children's, parents', and teachers' ratings of child behaviour. Differences were also found in self-descriptions: participants with disruptive behaviour were less likely to describe themselves positively than participants without. Our research finds no evidence of PIB among older children with disruptive behaviour and suggests that language competence should be considered more closely in future research.