In Taiwanese private adult education institutions, classes may continue over several years. For that reason, it is not possible to design the class based on the curriculum of the school education institutions. In this study, we use the Trajectory Equifinality Approach, and, focusing on adult Japanese language classes that continue for a long period, analyze in what ways a mid-career teacher has transformed the design of classes. The result of the analysis was that the growth of a teacher involves moving from a teacher to student relationship to a relationship of equal participants in the class. Additionally, it is suggested that, as part of this relationship, teacher carry out class design in collaboration with students, and create original value for that class.