A special school, or special purpose school, is a school catering for students who have special educational needs due to learning difficulties, physical disabilities, autism or social/emotional disturbance, or who are in custody, on remand or in hospital. Special schools may be specifically designed, staffed and resourced to provide appropriate special education for children with additional needs. Students attending special schools generally do not attend any classes in mainstream schools. The schools cater for students with mild, moderate and profound intellectual disabilities, for deaf and hearing impaired students, for students with autism spectrum disorder, and for students with a physical disability. Class sizes at specialist schools are smaller than at mainstream schools, and there is a much lower ratio of teaching and support staff to students. Some specialist schools also have therapists on staff. Specialist schools generally already have an accessible environment and curriculum for their student population; this may mean that there are limited subjects on offer.