The school performance is a multidimensional phenomenon determined by the student, the school and the socio-economical context in which they are immerse. In order to measure the performance of the educational institutions, the Ministry of Education applies a set of standardized tests which form the Measurement System of Quality in Education, SIMCE for its initials in Spanish. There are some factors which determine the performance in the SIMCE. Along this line, many authors hold that the socio-economical level of the students is the most important one to explain the school performance. However, the data indicates that, not only the dependence of the educational institution but also the geographical locationwhere it is located affect the school performance. This research aims to determine which are the best predictors in the SIMCE score of mathematics in educational institutions of the Araucania region. The nested data will be modelling by using a Generalized Linear Mixed Model.