There is currently controversy surrounding the effectiveness of universal versus selective prevention in eating disorders (ED). The present study aims at evaluating the effectiveness of universal school-based ED prevention administered to female secondary school students (n = 349). Students received either the full prevention programme (learning basic concepts of nutrition, criticism of aesthetic models of beauty emphasising extreme thinness, media literacy (ML)), a partial version of the programme (without nutritional education), or no prevention programme. Students were also classified on the presence or absence of distinct risk factors for ED: Early menarche, overweight, dieting, negative attitudes to food and perceived pressure to be thin. Pre-test data were collected 1 week prior to implementation of the prevention programme, and post-test data were collected on the last day of the programme. Results suggested that both the full and partial prevention programmes reduced perceived pressure to be thin and improved eating attitudes and knowledge of nutrition in all the participants (regardless of risk); however, greater effect sizes were found among particular high-risk groups (early menarche, overweight and highly influenced by aesthetic models of beauty emphasising extreme thinness). School-based programmes of universal intervention may have an important role to play in the prevention of ED.