Dialogue has been characterised as a communicative pattern that supports critical learning in education. Seeking to analyse this relationship, we investigated the interaction between teachers and students in two classes, a Third Grade and a Fifth Grade of São Paulo State public school. During the interaction, we identified a variety of dialogic acts; however, it was also possible to identify acts that obstructed the dialogue. In this article, we define and characterise non-dialogical acts and their connection with the students' participation in mathematical activities. By non-dialogic acts, we mean acts that obstruct the dialogue or turn it into another pattern of communication.