A lower secondary school student undertook the role of a science teacher in two elementary schools. We analyzed the contents of these classes. In addition, we analyzed the contents of the lesson study discussion performed later. The decision to use a lower secondary school student in the role of science teacher was made in accordance with the principle that learners perform well. The student did talks by "the experience exchange case" in a lesson study discussion. The student participated in the talks as "teacher," "professor," and "learner" in a lesson study discussion. It is important for...