The proposed numbers of children involved are not likely to be high enough to substantially effect the results at the local state schools.
A school near me has an A Level class with 4 children in it, if they lose one then they lose 25% of the students sitting that subject.
If the child that goes is the one predicted to be A* and the other three are B grade that is a substantial impact.
BTW even academically selective private schools do have some SEN children.
Yes, they have academically bright SEN children, they don't have the children with severe behaviour issues.
I wonder if these funded places can be withdrawn for poor behaviour?