when did inclusion begin?

Answer 1

I'm not sure if it was the 1975 law (Education of All Handicapped Children Act) or the 1997 law (Individuals with Disabilities Education Act) but one of those two laws required that a student with a disability receive a "free and appropriate public education" in the "least restrictive environment". The "least restrictive envrionment" clause requires that special education students be mainstreamed as much as possible, and segregated as little as possible.