The purpose of this study was to examine how Ayo, an ADHD returnee student, gradually improved his ADHD symptoms and psychosocial development through the assistance of residential care in his third grade of middle school. To identify the factors and process, the researcher conducts qualitative research through semi-structured interviews and documents. The research findings are as follows: Firstly, the assistance of residential care includes care and protection, acceptance and forgiveness, friend-like teachers’ company, patience modeling, dialogue and illumination, and (f) various exploration and learning approaches. Secondly, care, protection, acceptance, forgiveness, friend-like teachers’ company and patience modeling are conducive to building a relationship of care and trust for Ayo. Besides, care and protection can diminish Ayo’s behavioral deviation. The patience modeling promotes Ayo’s self-exploration and emotional control. The teachers’ dialogues and illumination facilitate Ayo’s self-awareness and develop his problem-solving skills. Moreover, various exploration learning approaches are favorable to Ayo’s potential, vision and self-exploration. Thirdly, in addition to the abovementioned six factors, incremental improvement in his mental function and the institutional change are the other two contributing factors for Ayo’s growth. Lastly, during placement, Ayo’s improvement includes explicit aspects, such as outer emotional control and behavior, and implicit aspects, like inner empathy and self-awareness. Based on the above results, relevant discussions on the assistance of ADHD teenagers are conducted and the following suggestions are offered in this study.