ABSTRACT – The Brazilian Public School Math Olympics (Olimpíada Brasileira de Matemática das Escolas Públicas, or OBMEP) has been held yearly since 2005, aiming at motivating students to study Mathematics and improving basic education. In this paper we evaluate the OBMEP’s impact on school performance in Mathematics, using regression combined with propensity score analysis, and do a cost-benefit analysis. The results show that OBMEP has a positive and statistically significant impact on school performance in Mathematics among nineth-graders. This impact increases for schools that participate in repeated editions of OBMEPs and is larger in higher test score percentiles. The cost-benefit analysis shows that the benefits of OBMEP in terms of the participants’ future income outweigh its costs.