Guevara Benítez, Y., Hermosillo García, Ángela, López Hernández, A., Delgado Sánchez, U., García Vargas, G.R. and Rugerio Tapia, J.P. 2008. Mathematical skills in students from a low social and cultural stratum. Acta Colombiana de Psicología. 11, 2 (Jul. 2008), 13–24.