Students with disabilities can have a particularly hard time making the usual transitions that take place in the educational process. When a student moves from one educational setting to another, it is a time of anxiety. If that student has a disability, the anxiety is multiplied. The new environment may have to be physically adapted. New classmates will have questions, and new teachers will need information on how to best help the disabled student progress and become an interdependent part of the new classroom or school.
Many people see it as an equality issue.
Others see it practically - some children aren't able to learn what they need to learn in regular classes. Whether or when disabled children are mainstreamed into the general school population is an issue that must be addressed for each child. Some students do just fine entering the general population at a young age. Others benefit by going to special classes for a few years and then moving into mainstream classes. The important thing is to make sure that mainstreaming is right for the individual child, rather than being done as a policy decision.