Definitions
In order to discuss the concept of inclusion, it is first necessary to have a common vocabulary. Research Bulletin Number 11, 1993, from Phi Delta Kappa's Center for Evaluation, Development, and Research provides a useful set of definitions. The following have been edited for clarity.
Mainstreaming
Generally, mainstreaming has been used to refer to the selective placement of special education students in one or more "regular" education classes. Proponents of mainstreaming generally assume that a student must "earn" his or her opportunity to be placed in regular classes by demonstrating an ability to "keep up" with the work assigned by the regular classroom teacher. This concept is closely linked to traditional forms of special education service delivery.
Inclusion
Inclusion is a term which expresses commitment to educate each child, to the maximum extent appropriate, in the school and classroom he or she would otherwise attend. It involves bringing the support services to the child (rather than moving the child to the services) and requires only that the child will benefit from being in the class (rather than having to keep up with the other students). Proponents of inclusion generally favor newer forms of education service delivery.
Full Inclusion
Full inclusion means that all students, regardless of handicapping condition or severity, will be in a regular classroom/program full time. All services must be taken to the child in that setting.
In addition to problems related to definition, it also should be understood that there often is a philosophical or conceptual distinction made between mainstreaming and inclusion. Those who support the idea of mainstreaming believe that a child with disabilities first belongs in the special education environment and that the child must earn his/her way into the regular education environment.
In contrast, those who support inclusion believe that the child always should begin in the regular environment and be removed only when appropriate services cannot be provided in the regular classroom.
http://www.weac.org/resource/june96/speced.htm