We have focused our research on studying the interactions arising from activities in a virtual learning environment on applying proportion in working out indirect measurement. The aim of the research is to analyse the effects of the interaction among students arising throughout the communicative process, when they see their work in a forum. In this situation, the context included in the mathematics virtual learning environment has a particular importance, offering opportunities to the students to express their reasoning, both to the tutor and to their fellow students, with the express intention of providing the opportunity to build knowledge, both socially and personally.