Science-learning research has addressed the analysis of discourse dynamics in classes oriented towards student-centred learning environments. One aspect not much investigated is the progressiveness of that discourse. For progressiveness to exist, interactions must tend to be symmetrical and power imbalances in dialogue must be reduced to a minimum. Also, a real dialogue must be established between the worldviews of participants. In this article we investigate this topic by analysing two sessions on thermodynamics taught by the same teacher (years 2016 and 2017). In both, the teacher presents the same problem situation. After the first session, and before the second one, the teacher analyzed her own videos with the purpose of designing classes with a greater dialogical component. The research carried out seeks to describe the changes in the teacher's actions and how these are articulated with the changes in student's interactions. For the analysis we used a social mechanism identified by Clarà (2019) to describe progressiveness, which consists of a series of iterations of the sequence (Direction) [right arrow] Inference [left right arrow] Observation [left right arrow] Consensus [right arrow] Fixation. Through this model, we were able to account for progressiveness in collective inquiry, and also to distinguish more and less fruitful teacher-interventions to foster it.