The teaching and learning of mathematics cannot be understood without considering the resolution of word problems. This kind of problems not only connect mathematical concepts with language (and therefore with reality) but also promote the learning related to other scientific areas. In primary school problems are solved by using basic arithmetic rules and in secondary school, the purpose is to generalize the resolution procedures through putting in practice algebraic procedures which turn to be more effective in terms of resolving word problem. This study attempts to analyse the procedures employed to solve mathematical problems by a sample of students in 9th and 10th grades of High School (N=406) from the Basque Country (Spain). For this purpose, the procedure used by the students when resolving three mathematical problems was examined and classified in three categories. These categories are related to the utilization of arithmetic rules or, as the case may be, algebraic procedures. The results indicate a significant relationship between the procedure used to solve the problems and educational level of the students. Educational implications of the findings are discussed.