if it's not because he finds school work difficult then what are his thoughts on school work? sounds like there's something he can't handle and he's acting out in this confrontational way.
when you ask him to do things at home is he doing something else at the time? i wouldn't want to leave what i was wanting to do for something someone else wants me to do (especially if i really didn't want to do it in the first place) would you? just because he's a child doesn't mean to say he doesn't have a right to feel this way too, does it?
how about a relaxed conversation, while doing something he enjoys, something where you aren't eye to eye (some kids find eye to eye confrontational and can't say what they want to say) and telling him you're there for him and really want to hear how he feels about things. it may not work first time, as it may be new to him, but keep trying and i'm sure it'll work because you're his parents and you love him, just let him know.
hope you are all relaxed and smiling soon.