Children's reports of the perceived seriousness of disruptive classroom behaviours were examined from their own perspective and from their perceptions of their peers' beliefs about the same behaviour. Two hundred and seventy-six (116 female and 161 male, M[subscript age]?=?11.00?years, SD[subscript age]?=?1.29) children recruited from a primary and a secondary school in the UK completed measures of the perceived seriousness of disruptive classroom behaviours from their own perspective and also their beliefs about their peers' perceptions, social desirability and social behaviour. A three-factor structure of disruptive classroom behaviours emerged encompassing: Imprudent behaviours, negative behaviours and expressed emotions. Children judged the disruptive classroom behaviours as more serious compared to how they thought their peers would judge the same behaviour. Gender and age differences also emerged. The findings support the conclusion that children regard disruptive classroom behaviours as more serious than they believe their peers do.