I would like to know if it would be possible to sue a school system for not taking the appropriate action to prevent bullying a disabled student?

It would be worthwhile to consult with an attorney with civil rights and/or disability-related experience. The short answer is it may be possible: North Dakota has an anti-bullying law; also, there are laws at federal and state levels preventing discrimination against the disabled in education. It is possible that bullying which negatively impacts the student's education, especially if such bullying falls into a category prohibited by the state's anti-bullying law, would give rise to a civil rights-related claim.