We analyse the effect of violent crime on students' results in Costa Rica. The combination of PISA data and highly disaggregated information on crime at the district level is a main contribution of this article. Our methodological approach provides also some novelties in the field, the most important being the use of a simultaneous equations model solved with instrumental variables. This allows us to obtain unbiased and efficient estimators in the presence of simultaneity between education and crime. We conclude that exposure to crime, measured by the homicide rate, has a negative and significant impact on academic achievement. This effect is particularly important in the case of students attending schools situated in districts with a lower social development.