There are a broad range of rehabilitation programs but results differ significantly among them, from positive to no-effect programs –and even to negative-effect programs. Hence, in order to guide policy, it is necessary to find out the features that should be present in programs for inmates to guarantee positive effects. We used a random assignment to evaluate an innovative rehabilitation program –rugby classes offered by players of the national team- for incarcerated offenders in an overcrowded prison in Uruguay. We find the program positively influences inmates’ behavior, lowering the consumption of drugs. Also, studying the mechanisms behind these findings, our results suggest that the program fosters healthier conduct and positive social attitudes. After studying the criminogenic attitudes addressed by this rugby program, we suggest lines for policy.