Cecilia, our experience with this is that our DS8 has Asperger's Syndrome; people with AS tend to misread social roles and not understand that it's actually a hierarchy, with people having different kinds of power based on their socially assigned roles.
We openly discuss this sort of thing all the time, both with examples ("today my boss told me X and I wanted to do Y but I had to do X") and with literal explanation ("In our family, parents are in charge; you have to do what they say even if you don't want to."). We practice using different kinds of disagreeing words using a polite tone, and we talk about which kinds of words you are allowed to say to whom. For a kid with AS, this is best learned by rote, right in the situation; I (or his teacher) give him a script to say, he uses it, and gradually it becomes part of his repertory of things he knows how to do.
With coaches, piano teacher, etc: does your DS respect them, or just go along because he likes what they have to offer? Our DS's other big issue is "non-preferred" activities-- it is much more difficult for him to follow instructions he's not intrinsically interested in. Yes, that's a little true of all kids, but they are generally more flexible and compliant, and their awareness of the teacher's authority means they go along better. My DS's AS makes following certain instructions feel like a huge obstacle, and he can get obstreperous.
School has been supportive and we are making headway on these issues, again through rote practice: in every situation he encounters, making sure he does it right, and if he doesn't, backing him up to practice the skill of accepting the instructions before going on. Tedious work, but ultimately effective.
My feeling is, if you pull your DS out of school, it might be easier for everyone in the short term, but he'll have fewer occasions to develop the skill of doing what he doesn't want to do.
Which is not to say you should leave him with inappropriate work-- that should be addressed in your plan, too.
HTH,
DeeDee
Edited to add: We found it not enough to talk about "being respectful"-- that kind of general information wasn't useful for DS. We had to specify: "to be respectful, use a pleasant voice, have a pleasant expression on your face, don't use angry words but rather use calm words, choose words that won't make the person mad," and so on.
Last edited by DeeDee; 02/01/11 01:57 PM. Reason: added postscript