Bullying is a considerable problem among school students, and school-wide positive behaviour support interventions are regarded as helpful in addressing it. One approach is the CATZ Cross-age Teaching Zone anti-bullying intervention. The present study assessed the social validity of the CATZ anti-bullying intervention among a sample of 9-15-year-olds in a pre-post experimental design (N = 817, of which 546 experienced CATZ). Overall, participants expressed moderately positive views of the CATZ anti-bullying intervention, and these became significantly stronger following direct experience of it. Among participants who experienced the CATZ anti-bullying intervention, social validity ratings predicted a greater willingness to engage in it in the future. Alongside the extant data for its effectiveness, our findings support the wider use of the CATZ anti-bullying intervention in schools, and suggestions for how this might be brought about are discussed.