Anti-bullying commitment across school communities is seen as crucial to the effectiveness of interventions. This exploratory study used a mixed-methods design to investigate bullying behaviour, intentions and aspects of the classroom ecology within the context of an anti-bullying initiative that was launched with a declaration of commitment. Across the sample of 14 primary school classes, containing 338 children aged 8-11 years, changes over time in peer-assessed and self-reported bullying and victimisation were found to be associated with changes in pupils' sense of school belonging and perceptions of their classroom climate. Using a newly-developed theory of planned behaviour measure, changes in bullying were found to be associated with pupils' intentions and perceived control with regard to engagement in bullying behaviour. No differences were found between intervention and comparison classes on any of the pupil outcome measures. However teachers of intervention classes reported a relative increase in perceived control over undertaking anti-bullying work with their class. The role of the class as a meaningful unit of analysis in the investigation of ecological-systemic bullying interventions in primary schools is highlighted.