With respect to students on an IEP who are being disciplined, sometimes disagreements will arise between the child's parents, who believe that the problem behavior is a manifestation of the student's disability or a school's failure to properly implement the IEP, and the rest of the IEP team, who believe this not to be the case. If this happens, it is a serious problem, and the school district is going to have to make some very important decisions. Things for the district can turn very messy very quickly - not to mention very expensive - if there is a determined parent, and the district must make a decision as to whether it wants to have this fight or wants to work out some kind of a compromise with the parent.
Unfortunately, bullying at school is a problem that parents and students deal with far too often these days. Parents whose children have been bullied at school are well-advised to deal with the problem as soon as it comes up. Otherwise, it will not be seriously or adequately addressed.