Lots of lovely examples of children who take ND children under their wings occasionally. The difference in my opinion is the expectation in this case is that it's not occasional, it's not a couple of PE lessons a week etc. It's every day and if they don't cooperate they are bullies. Nice.
I'd always expect my children to be kind, I would hate them to be nasty to anyone, but I'd draw the line of them being told that they have no choice to who they talk to, or sit with during their lunchtime. Im struggling with the "sits quietly" part baring in mind he wants to be with the child who talks to him - but that's been asked a few times and ignored. I wonder how quiet he is. My DS has SEN , he sounds very similar. He's generally very quiet, but has very distinct interests in life and is in his element if he can find someone who happily talks about his interests. Would I expect that person to deal with him every day? No I wouldn't - that's not fair. I'd like to think that person would chat to him from time to time, but I wouldn't demand daily, and I'd explain that to DS as best I could (not easy I know)
It's hard to really pull apart what the story really is here OP, obviously you are vehemently going to defend your boy, of course you are, but I wonder how long this has been going on, how long the group have gone along with it, how the "you can't sit here" was presented to him, how much was he keen to have the attention of this child, how much that child can cope with it - I'm very introverted, I don't have SEN but would struggle massively with having someone wanting to talk to me every day.
I find the schools response interesting, they need to support your DS, but as I said up thread, I wonder if there is a reason they won't encourage this friendship.
I know what it's like to have a child with SEN. My DS has complex medical and learning/social needs. He's the opposite to your son OP, in that he's much more taller than his peers and has gone into puberty early so is having to deal with feelings/hormones when really he's a young boy. Most people expect him to cope with more due to the fact he looks like a young adult when actually he's 12. I'd wrap him up in cotton wool if I could, but I can't 