Quoting Cassie♥:" like i said no one was expecting physical force... maybe threatening to call the cops or his parents or something? saying oh your making a bad choice does nothing... and he is a kid."
Didn't he leave b/c they were in the process of calling his parents? Or just about to?
And you said this happened on the school bus, which I am assuming is at the beginning of school....I imagine he's not the only child who attends this school and from the sounds of it, they were working as quickly as they could, the mornings are extremely hectic at most schools.
Either way, I hope he turns up soon and that he's alright, but I'd personally pass the blame on the child himself and the parents, not the school system.