Itsuki Kubo has been an elementary school teacher in Kyoto City for a long time, and further developed the teaching materials and educational methods developed by Hiroshi Kishimoto to enable the formation and mastery of basic academic ability, and is a school with the theme of academic ability formation for all children.He is a practitioner and a theorist who has brought to fruition the practice of making.He has also raised the educational skills and practical research (training)necessary to improve the practical competence of young teachers and further develop them as teachers. So why was Kubo able to make such a proposal in terms of both theory and practice? In this paper, based on this awareness of problems, we clarified the growth and competence formation process of Itsuki Kubo as a teacher based on life history research.