Consensus building is an important activity for various people to resolve problems through cooperation. In recent years, progress has been made in studying consensus building in elementary-school Japanese language classes. However, there is no standard positioning or definition of consensus building, and the developmental stages of consensus building ability have not been clarified, such as the kinds of consensus building possible in each grade. Thus, it is extremely difficult to establish consensus building discussion goals and instructional guidance. Therefore, this study aimed to define consensus building in elementary-school Japanese-language classes with discussion-based learning and propose a process model of consensus building. First, based on prior research on consensus building in Japanese-language education and on Straus’ theory of organizations, the importance of the concept of consensus building at each stage in the process was identified. Next, by analyzing child protocols, consensus building as a learning theory was defined as “exploratory consensus building,” with the following characteristics. (1) With “exploratory consensus building,” the consensus-building process can be retroactively traced back. (2) Agreements based on “exploratory consensus building” can be reached by means other than a majority vote. (3) Finally, “Exploratory consensus building” agreements are no more than provisional at all times. In view of the above, the study proposed a process model of elementary school‒level“ exploratory consensus building.”