The aim of this study is to understand the importance of the Opportunities-to-Learn (OTL) offered by teachers in the classroom in facilitating the acquisition of mathematical competence (CM) of their students. Accordingly, our goal is to find and describe the possible relationship between OTL and CM. In this paper we present the theoretical model OTL-CM which seeks to describe, explain and predict the phenomena of teaching and learning, in terms of how certain OTL (offered by teachers in their classrooms) may favor the development of certain CM. This model can be applied in observing teachinglearning settings as an instrument that can help explain and interpret them.