This research aims to compare teachers’ postures in arithmetic problem solving sessions with the 3 cycle of primary school. The video analysis of sessions in a class of CM2 focused on the relationship between the use of different ‘learning vectors’ (software, school manual, substitute sheet, mathematical rallye) and the teacher’s oral modes of intervention, and between his or her stated intentions and observable practices. Regardless of the vectors used, the teacher states that he wishes to give priority to learners’ activity. However, this convergence of intentions prevents diverging practices. As part of a mathematical rally, we note that the teacher respected the rules inherent in the situation in order to let students carry out their resolution activities. As regards the use of software, while the teacher claims the necessity of the pupil’s activity and peer-to-peer mentoring in the use of CTBs, we paradoxically observe a much more prominent mode of oral intervention by the teacher in the CTBT room than in the classroom, in resolution with paper and pencil. On the basis of the pedagogical styles described by Drevillon (1980), the classroom session would be predominantly active-flexible, as the teacher accepts the dialogue, listens to his students, asks them to go to the table to present their solution to their peers, while the session conducted using the CTBs, which is marked by a strong teacher’s stewardship, appears rather to be predominantly impositive-flexible. Self-confrontation interviews (Clot, 2000) with the teacher highlighted the influence of learning vectors on teaching practices.