1 child can impact on a whole classes learning.
I had a very tricky class this year, with two significant challenges amongst about 7 others. The two took up about 50% of my time, 80% of an LSAs time.
The other day when they came in for transition, the children who went into other teacher's classes were only interested in whether they were in a class with those two significant challenges. When they found that they weren't, they were cheering.
If I'd known that my child was in a class with children like that, in terms of the amount of adult time they use, I'd move them out of the school. This school is great for behaviour management, but there is only so much money, and almost no input available from outside agencies to support. By the time they get to you (2 year wait), you've tried everything they are about to suggest.