Every child does have a right to an education, even the ones causing a disturbance. The schools have channels to educate these students differently. The problem is are we funding those channels. When a school is told to educate all these kids by law, and the government says but we will only fund it 50% of the way. The school has to figure it out. I am not an apologist, but will acknowledge that it is difficult.
Also, kids get expelled all the time. More than not it is the kid who is in special needs, because he is seen as the problem.