In Ireland, an increasing number of students with special educational needs are leaving mainstream schools and enrolling in special education schools. A comparable context is countries that share an inclusion ideology and are at the implementation stage of inclusive education. The authors sought to investigate the reasons why students aged 12+ are leaving mainstream education and transferring to special schools, and to identify what burden this places on the special schools. Data were obtained from questionnaires sent to 54 special school principals. These administrators reported on their experiences with 246 transfer students. Descriptive analysis, Kruskal–Wallis, Mann–Whitney U, and exact tests of significance were conducted between school groups and level of agreement with perceived difficulties. The principals reported an increasing trend (40% over 5 years) in students enrolling in special schools. The main reason given for the students leaving mainstream schools was the failure of mainstream schools to meet their academic, social, emotional, behavioral, and access-to-health resource needs. Adjustment and integration problems resulted from a lack of transition planning, entering too late into the special school curriculum, and an over-dependency on supports. Students were reported to display a lack of self-confidence, classroom disengagement, peer interaction difficulties, and challenging behavior, and these dysfunctions were attributed to the mismatch between the students' educational and other special needs and the educational environments.