The problem with this is the snowball effect. Every kid with any (in most cases made up) disability is going to demand to bring their dog to school. "I have ADHD and can't concentrate without my dog" "I have Oppositional Defiant Disorder and I won't cuss out the teacher if I have my dog here" and on and on. Imagine a big school with 2000 kids and atleast 100 bringing their dogs. This is what we're opening ourselves up for.
With this childs disability he shouldn't be mainstreamed anyway. He should stay in a special school for Autistic kids.