Objectives: In the process of transition services, the active participation of teachers and parents is an important key to the successful employment and independent living of students with intellectual disabilities after leaving school. Methods: This study adopted a case study method, taking a high school in Taiwan that has a good transition service as an example. The research participants included four special education teachers and four parents. Data were collected through semi-structured interviews, archival documents and research diaries. Results: The results showed that parents' active participation in transition activities, employment-oriented vocational curriculum planning, building parent-teacher partnerships, understanding students' strengths and abilities, and support from social resources were the key factors for the successful post-school transition. Conclusions: This study also showed that early participation in transition planning, joint participation in transition planning by parents and their children and the development of independent living skills were the transition service needs for students with intellectual disabilities.