What I did for my son was to hire a shadow. His major problem was running away from the classroom, but as a side benefit, the shadow was there to intervene whenever he had violent impulse. If I were you, I'd wait until the next violent outburst, and then when the hand-wringing committee convenes, suggest that a shadow be hired. If the parents can't/won't pay, then they might have to leave the co-op, but your desire to not pitch this child onto the street when you see him making progress at your school is a GOOD thing. Don't be ashamed of that!