So, if you chose to send your child to a boarding school then I'm curious as to why you chose to?
My son has SEN. I got so tired of him being illegally excluded, being taught in corridors away from the 'normal' children, being excluded from invitation to parties, excluded from life, that I took him out of mainstream school and Home Schooled him for nearly 2 years, during which time he went from a child who was terrified of people to a really quite able student. I had constant abuse from the LA, but, as they refused to entertain the idea that he needed to be in a special school, they had no case.
We moved to a country where HS is illegal, so he was forced to attend school again. He was physically attacked, spat on, taught in the corridor, illegally excluded and we'd had enough. My DH's employer would pay for DS to go to a special BS in the UK, so we took the opportunity. He was taught in classes of 8 children, he was able to concentrate on subjects he was good at, so his self esteem was built up and he was then able to tackle things which had eluded him before. He started playing sports, because he didn't have teachers and other pupils taking the piss out of him all the time. He tried new sports because he had built the confidence to try things. He has friends. Lots of them. The friendships he has are a little kooky, but they are real.
We were told, categorically that he would never be able to take any 'real' exams, this summer he took 8 GCSEs he will get an A-A* in one of them.
It broke me, every time he had to go back, but, I knew I was doing the right thing by sending him. Even when we moved back to the UK, and I made inquiries about him attending a SN day school, we were told that he would have to go to a MS one, so we demurred. If we hadn't had a government who continually experimented with making children for whom MS was not suitable go to MS schools, then the argument would have been academic, but, as so many SEN placements and schools have disappeared, then some of us are left with little choice but to send our children to BS. With hindsight though, if I had to do it all again, I would have sent him anyway.