I spoke with Alex's teacher and I have a much clearer idea of the kind of support she's suggesting. I still need to talk with our behaviour specialist and tutor to see if we can make it work, but at least I'm clearer on what I'm asking for.
Alex is a smart cookie and when he's transitioned to new environments in the past, he will "underperform" and set up lowered expectations. With some support from people who are already familiar with him, we may be able to keep him from regressing too badly.
That's much more manageable that pulling him out of school for half-days (although we may still have to do that if that's the only time available).
We'll take it one step at a time. And we'll get there.
On the plus side, I just found out that both boys have been approved for summer respite funding from Autism Ontario. That will definitely help out with costs for the summer.