Resumen: The purpose of the study is to assess the effectiveness of a school-based programme to improve knowledge, attitudes and beliefs about doping. 540 adolescents (aged 12-13 years old, 50% boys) took part, from eight Spanish schools. Three hundred and thirteen of these were in the experimental group and the rest formed a control group. Six sessions were held, based on international recommendations, during the Physical Education classes, and were assessed with the Questionnaire on the Anti-doping Intervention programme. The principal results showed that the knowledge, attitudes and beliefs about doping improved in the experimental group compared to the control group, for the whole of the questionnaire (p<.001, Eta2=.03) and specifically for the factors Concept (p<.001, Eta2=.004), Utility (p<.01, Eta2=.02) and Sport and doping (p<.01, Eta2=.01). But there were no benefits observed in the factors Methods and Origin of the behaviour. In conclusion, school-based programmes may be useful for improving knowledge, attitudes and beliefs about doping among adolescents. Idioma: Inglés DOI: 10.14198/jhse.2019.144.10 Año: 2019 Publicado en: Journal of Human Sport and Exercise 14, 4 (2019), 813-820 ISSN: 1988-5202 Factor impacto SCIMAGO: 0.403 - Physical Therapy, Sports Therapy and Rehabilitation (Q2) - Sports Science (Q3)