This paper seeks to explain academic achievement in Mathematics based on individual student characteristics. The study takes the case of Paraguay, a country below the regional average in recent international assessments of learning achievement in mathematics by basic-level students (students in Educacion Escolar Basica). A questionnaire was administered to 899 students of the third cycle of basic-level education (7th, 8th, and 9th grades) from both public and private schools in the district of Concepcion. Two statistical modeling techniques were employed on observable variables: decision trees and multiple linear regression. It is concluded that academic achievement in mathematics is largely explained by students' learning in a classroom setting and perception of their own ability.