There were two special schools here when I was a child - one for moderate learning disabilities with 160 pupils, and one for severe with 70.
They wet both closed and merged into one school which has 180 places at primary and 205 at secondary age.
Both are completely full, parents are desperate for places.
My own son has been there since reception. We had to fight for a place. The local authority thought a non-verbal incontinent child who needed constant supervision (including all breaks and lunch time) would cope just fine in mainstream.
They really don't like spending the extra money unless they are forced to.
There is no way he would have coped, and it would not have been fair on him or the children who would have had to share a class with him.
He's done fantastically well at his school. He's 16 now and has done entry level exams. 
Inclusion is great for some but it should not be seen as perfect for everyone.
I Home educate my youngest as I know he wouldn't cope in a mainstream secondary but there's also no way he would get an EHCP, and there are no schools that take academically able children with autism unless you go through many many battles.