If he is asking to do the same work as the other children, it is a fair bet that either the teacher has commented about or made an issue of the fact that his work is different, or that the teacher is asking him to do his "challenge" work during a time when the other children are doing something that he would like to be doing, too. This is not ok.

Or it may be that he doesn't want to do it because his "challenge" work is *twice as boring* because it still isn't teaching anything but takes twice as long... if he is getting pages of two and three digit addition worksheets, but is capable of working at 7th grade level, I can see why he'd rebel.

I think that it is important to find out what this supposed "challenge" work is before you meet with the IEP team again, or at least make sure that the teacher brings the same work your son refused to do to the meeting with her.