This paper argues that a teacher should and can be not only the organizer of a lesson as well as participant in a dialogue who has the equal right with pupils vis-à-vis the truth of the learning material in order to make lessons dialogic. To analyze such a teacher's way of being in the lesson, the concept of a triadic relationship among pupils, learning material, and a teacher was introduced. The teacher can learn something new in the pupils' learning material as the pupils can do. The teacher can discover an unknown question that she/he does not know its answer or even its existence in pupils' wrong or irrelevant thoughts about the learning material. This sort of teacher's learning makes classroom lessons dialogic as pupils and a teacher exercise the equal rights vis-à-vis the truth of the learning material in the lesson. Here, pupils and teachers learn about the learning material from each other. The importance of this sort of teacher's learning for dialogic lessons has been rarely emphasized in dialogic pedagogy research. These arguments are advanced in this paper based on the analysis of the Japanese elementary teachers' knowledge of practices. This paper focuses mainly on the pedagogical view named Saitou pedagogy developed by Kihaku Saitou and his colleagues, and studies their thoughts and classroom lessons to investigate teacher's work to make lessons dialogic. To provide a theoretical basis for the analysis, theories of dialogue, developmental psychology and dialogic pedagogy were reviewed to understand how these theories had studied the triadic relationship and were compared with Saitou pedagogy. The result demonstrated that Bakhtin's perspective on the dialogic author was useful in analyzing the teacher's way of being in Saitou pedagogy. It was also suggested that Saitou pedagogy's view of the unknown question would give Bakhtinian theories of dialogue a hint for new area of study.