In kindergarten, since the DX and IEP take time to establish, the lone teacher has no help in the classroom at all. A 20 to 1 ratio is NOT sufficient with a special needs child and no aide to help.”
Until the kid is diagnosed, he's not mainstreamed. He is a regular part of the regular class. Once his diagnosis is confirmed, appropriate placement is determined. That can be anything from a regular class with only one teacher to a fully self-contained classroom with a very few students (I was offered a job in a class with 4 students, 2 aides, and me as the teacher).
As for the problem being with mainstreaming kids, think of it from this point of view for a moment: Do you want a kid in a classroom full of kids who don't behave well, learning their behaviors, or in a classroom where the other kids do behave well, to learn from them? There are pros and cons, but for most kids, it is more beneficial to the disabled child to see how how other normal kids act, and learn to imitate them.
And some will need to be pulled out of even a lab setting, and tranquilized. You've run into adults like that, in your life, I'm sure. I certainly have.
Mainstreaming works great for some but not all. The problem is that often the parents of the special needs child aren’t always given a voice. Even if they believe their child would function better in a special education school they often get overruled. If they would do this on a case by case basis evaluating the needs & abilities of each child, mainstreaming would work much better. But we also have unqualified teachers anxious to get these kids for the extra somethin’ somethin’ in their paychecks. Then it becomes a disaster for everyone.
So, for the benfit of a single child , the rest of the kids get to be role models, no matter the cost to their already failing education? Not for me.
As a kindergarten aide, I know first hand how much attention I have to devote to the special needs child that is being mainstreamed (dx and all!). If I turn my back to help another student...just to answer one question, I see a pencil whizz past my face in the direction of the other student. How about the child that doesn't get the teacher's attention immediately and starts banging his head against the wall? Shall the other students learn this sort of behavior from the special needs child? 5 year olds, after all, are great immitators and if the special needs child gets his way all the time doing these things, the others pick up on very quickly!