This ethnographical study aims to interpret how an intelligent tutorial system, geogebraTUTOR, mediates to the student's argumentative processes. Data consisted of four geometrical problems proposed to a group of four students aged 16-17. Qualitative analysis of two selected cases led to the identification of the development of argumentative competences by the students, as well as the level of influence produced to them. As regards the influence of geogebraTUTOR on the students, the study revealed that the interactions of tutor-teacher-student produced a significant number of mathematical learning opportunities of `thinking strategically' type; establishing figural inference conjectures and fostering the transition from empirical to deductive argumentations.