This paper presents the results of a non-experimental cross-sectional study conducted under a mixed explanatory design (with manifest and latent variables), in an indigenous school in a rural area and an urban school in Morelos (Mexico). The sociodemographic context of the schools of origin was considered as a predictor variable of Mathematics achievement in 6th grade of primary school, and the educational level of the parents and family support were considered as mediating variables. At the end of 6th grade, students from both schools answered a scale on family support and a short test on two mathematical competencies: Communicating mathematical information and Using techniques efficiently. The data were analyzed with two structural regression models of relationships between manifest variables (school context and parents' educational level) and latent variables (family support with eigh...