Going beyond simply measuring the effectiveness of a teaching approach with computer simulations during whole-class science instruction, we investigated the interaction between teachers and their students as well as searched for mechanisms in the pedagogical context related to teachers’ implementation of the intervention. Our quasi-experimental design involved having five teachers teach Newtonian mechanics with computer simulations to parallel classes of their upper secondary students. In the “Accustomed” condition the teacher decided how the lesson would unfold; in the experimental condition the lesson unfolded according to a pattern designed for “Peer Instruction”. We investigated the pedagogical interaction between teachers and their stu...