Objectives: To examine school-level relationships between deprivation and breakfast eating behaviours (breakfast skipping and the healthfulness of foods consumed) in 9–11-year-old schoolchildren and to examine whether attitudes towards eating breakfast mediated these relationships. Design: Cross-sectional survey. Setting: One hundred and eleven primary schools in Wales. Subjects: Year 5 and 6 pupils within the 111 primary schools. Measures were completed by 4314 children. Analysis was conducted at the group (school) level, with each school representing one group. Results: Deprivation was positively associated with breakfast skipping and consumption of ‘unhealthy’ items (i.e. sweet snacks, crisps) for breakfast. A significant negative association was found between deprivation and consumption of ‘healthy’ items (i.e. fruit, bread, cereal, milk). Deprivation was significantly inversely associated with attitudes towards eating breakfast. The relationships between deprivation and (1) breakfast skipping and (2) consumption of ‘healthy’ items for breakfast were mediated by attitudes towards eating breakfast. The hypothesis that attitudes mediated the relationship between deprivation and consumption of ‘unhealthy’ breakfast items was unsupported. Conclusions: Deprivation is associated with adverse breakfast eating behaviours amongst children aged 9–11 years, in terms of breakfast skipping and the quality of breakfasts consumed. Socio-economic differences in attitudes towards eating breakfast are apparent amongst this age group, and appear to relate to social gradients in breakfast eating behaviours. Research is needed to examine the causal nature of these trends and to elucidate factors underlying the development of socio-economic differences in eating-related cognitions.