My son was chucked into the mainstream aged 11, not long after Blunkett had decided that because he had a bad time at a special school, special schools/units should be axed...
So son went from being in a class of 6 in a special unit, with two teachers, TAs, everything calm and quiet... to a mainstream High School where he had to share a TA with numerous others, and all the noise and chaos, deeply distressing him. Still, am sure the government saved some money. 
Being mainstreamed might have suited Blunkett as a child but it did autistic kids no favours.
I was teaching several years earlier in another LEA where they started shoving SEN kids into the mainstream and over a few months, I went from having a class of 24 to a class of 30 (not good for any of the kids). Two of my SEN kids had badly clashing needs. I had never been trained although as the mother of two kids with SEN myself, was willing to learn how to help those kids. No INSET training. And that was in the days when you couldn't actually ask TAs to work as it might be 'demeaning' which meant I was running round like a blue arsed fly every break and lunch hour preparing the extra resources for my visually impaired child.
The mainstream classroom generally is not a place for kids with autism. But those legislating don't give two hoots about anyone with disabilities, as the recent tory attacks on the disabled have shown.