DGS specialise in extra support for visually impaired boys AFAIK - a couple of ds' friends in Y11 have moderate visual impairments.
There are other boys in his year who have HFA/Aspergers, and a boy in his year group who has ADHD. All of those families seem extremely happy with the pastoral care at DGS for their sons. That said, it does sound like there is perhaps the best provision for your friend's son at BETHS salsa. Good luck to him. I hope your ds is enjoying DGS...I cannot believe we are at the point already where we will be meeting my son's tutors to discuss IB options next term
those five years have whizzed by!