Two research questions are answered: how did teacher instructional skills develop during a whole school year? What is the influence of this development on the interactions between students during the co-operative learning moments? From the analysis, it appeared that the teachers' instruction changed from direct instruction to a more process and group-oriented coaching style, and that students started to work collaboratively, using the graphic calculator in an exploratory and investigative manner. This more process and group-oriented coaching style may have supported the change in the interaction pattern during this school year. The analysis showed that students gradually developed a more exploratory way of collaborating, confirming improved collaborative learning. At the commencement of the school year, students were focused on each other and did not argue much, while at the end, they were discussing with one another.