Lesson Study is a collaborative, cyclical and continuing professional development process, aiming at improving a lesson through critical reflection. This research is based on three cycles of Lesson Study conducted during a four-week workshop in Japan for 10 South African mathematics and science educators. A sub-group developed and refined a high school biology lesson on the blood circulatory system. The final goal of the process was to present the improved lesson in a real biology classroom in a Japanese high school. Two questions are explored in this research, 'As the Lesson Study cycles are repeated, how does the focus of the discussion change and to what extent does the quality of reflection in terms of insight and substance increase?', and 'In what way, if at all, does the discussion contribute to the improvement of the lesson?' In this research, we analysed the transcripts of three post-lesson discussions, one for each cycle of Lesson Study. The results indicate that both the focus of discussion and the quality of reflection changed depending on social context, hierarchical power relations among participants, and the perceived purpose of the session. Moreover, they show how certain comments contributed directly to improvements to the lesson. The results are discussed in the light of the theoretical conceptualisation of reflection used to analyse the data. We make some practical proposals as to how to enhance educators' participation in team lesson planning and improvement.