The current educational reform requires the professional development of teachers who can integrate the perspectives of special needs education and subject education. This paper aims to provide a foundation for the reform of the professional development of subject teachers. Specifically, we use a case study of a social studies junior high school teacher working at a special-needs classroom to explain the process of reflection on how he practiced, what ambivalences he faced, and what he learned through his review. There are three stages of the reflection process: technical, practical reflection, and critical reflection. The following two points are the results of reflection, which verbalized the tacit knowledge embedded in the practice and provided it as explicit knowledge. (1) Difficulties in gatekeeping to integrate the perspectives of special support education and academic education arise due to the structural factors of having various role conflicts. (2) Reflecting on the characteristics and challenges of one’s own view of disability from the concept of the “social model” may bring about a change in gatekeeping that integrates the perspectives of special support education and subject education. The reflection presented in the case study in this paper could be helpful information to improve the professional devolvement of subject teachers.