Whole-school anti-bullying programs are widely recognised as the best, evidence-based approaches to reducing school bullying. Despite this, few published studies have been conducted within high schools to systematically evaluate anti-bullying interventions using a control group design. To this end, a quasi-experimental study of anti-bullying interventions was conducted in four international secondary schools in Hong Kong. The four secondary schools were randomly assigned to: (a) a whole school curriculum intervention, (b) a combined Year 7 curriculum and shared concern intervention, (c) a shared concern only intervention and (d) a control school. The sample consisted of 549, year 7 students who anonymously completed a pre-test / post-test questionnaire. Results were analysed using several ANOVA procedures. When post-test composite bullying scores were adjusted for pre-test school differences, a highly significant main effect for schools was found (F = 7.70 p < .001). In further comparisons, a repeated-measures ANOVA showed the most significant reduction in bullying composite scores occurred when a whole school intervention was used (F = 10.73 p < .001). Bullying levels increased from pre-test to post-test over the school year for both the control school and the school that adopted a shared concern only approach. These results provide strong support for the need for high schools to adopt a whole-school preventative and management approach if they are to be effective in reducing student bullying.[Copyright of Australian Association for Research in Education (AARE) at http://www.aare.edu.au]