Hi Trepid.
Years ago I taught a class where there were 2 kids like your ds and the bully. At first the hitter got punished, but after a few times, I sat down to unpick it is bit further and the phrase kept coming back 'he was winding me up'
To be honest I wasn't very sympathetic at first, but I watched them for a few days.
Once I was watching, I saw that child A was quietly teasing and stirring child B all morning. Little commetns across the table. I think he tought some of them were funny, but child B didn't think so. Then they went out to play, child A said one more thing and it was the last straw, and so child B lashed out and thumped him.
So I was very clear to both boys. You both miss playtime. One for winding up, one for hitting. I also spent time with child B talking about alternative strategies to help him. (walk away, tell teacher, tell me after break, laugh etc)
I very quickly had child A's mother in wnating to know why he was being punished when he was the victim. I explained, she insisted that her pfb would never do that, I said he needed to learn not to wind others up.
It soon stopped. (not before she had bad mouthed me to every other parent in the playground)
My point is, it isn't always as easy and obvious for the teacher, especialy if the other child is clever. Go in and ask for meeting with teacher and HT. After a 2 day exclusion, they should be willing to do that. Explain what is goign on (not with ds present) stress that you support his exclusion for his behaviour, but that it is part of a bigger picture, and that the school needs to work on the bigger picture and help.
Sit down with ds and say some of the things you have said on this thread, that the bully doesn't want to be his friend, that he is winding ds up and then sitting bakc to see what happens. That doing as he asks isn't getting him a friend or into a group of friends, but is getting him into trouble.
Find some daft examples - if he asked you to pour a bucket of water over your head - would you? If he asks you to stand on one leg and sing twinkel twinkle - would you?
Then suggest some more serious examples - if he asked you to jump off the roof - would you? Why not? What about if he asked you to steal something that belonged to someone else? Would you? Why not?
Make a poster with him, one side - things I would do if asked - play football, join a game, lend a pencil. and on the other side, Things I wouldn't do - hit or kick, call someone names, etc etc, include a daft one to stop it being too heavy.
making a plan to make a good choice can really help kids to say no in the heat of the moment, because they have already made the decision.
At the end of the day you can look at the poster and ask him if he had ot say no today to something he was asked to do and congratulate him on sticking to his good choices