The research presented here evaluates the delivery of Happy Being Me (HBM; Dunstan, Paxton & McLean, 2017) with boys and girls in their first year of secondary school in the UK (Year 7 and after comparisons aged 11-12). HBM is a manualised universal prevention programme which aims to improve body dissatisfaction and associated risk factors. Risk factors studied here were internalization of the thin ideal, physical appearance comparisons, appearance conversations. Secondary outcomes measured were self-esteem and eating disorder symptoms Study 1 tested the effectiveness of HBM (n = 172) compared to a control group (n = 197) who received curriculum as usual. HBM resulted in significantly improved body satisfaction post-intervention which was maintained at follow up. There were no significant changes in risk factors. Study 2 compared clinician (n = 172) and teacher (n = 174) delivery. Students who received clinician-led, but not teacher-led, HBM had improved body satisfaction and this was maintained at follow up. Internalization of the thin ideal and self-esteem, improved in both clinician and teacher-led groups with small to medium sized effects. HBM can be delivered by clinicians independent of programme developers in a heterogeneous sample with positive effects on body satisfaction. Issues arising for wider delivery are discussed.