The purpose of this study was to evaluate the effectiveness of an intervention program aimed to develop fair play behaviours in a school Olympic Education program. One hundred and twenty six, 5th-grade students from 4 elementary schools participated in this study, 66 of which were in the experimental group and 60 in the control group. The results revealed significant improvement in the reported fair play behaviours, classroom support and autonomy, orientation toward play and intrinsic motivation of the intervention group. Follow-up assessment revealed that the effects were maintained two months after the end of the program. Overall, it appears that the fair play intervention had immediate and sustained effects on students. The results suggest that programs based on sound theoretical principles can be effective in promoting students' sociomoral development. (Contains 4 tables.)