Even if there is a daddy at home, the current paradigm is to place emotionally disturbed, violent children in a classroom, sometimes with a full-time handler.
I am not sure of the rationale, so I won’t hazard a guess.
The boy should not have been in a regular school. He belongs somewhere to get the help he needs.
‘Regular schools’ are required to take them. There is no somewhere else for them. And schools are required to have kids like him in the regular classrooms as much as possible. Which means that at least 50% of your kid’s teachers effort and attention are focused on that one kid. If the kid is really crazy, he might have a full-time aid assigned to him. But he’ll still be in you kid’s classroom.
This is not the school’s decision, this is the law as it now exists. Only the most extraordinary behavior might result in expulsion and even then, your school district will have to pay for his ‘education’. And if his misbehavior can be linked to his official handicap, say Oppositional Defiance Disorder, he can’t be expelled.