As a teacher, I think that at school kids can feel isolated when going through family upheaval. 10yr olds as you know as a parent are beginning to try to become "themself" instead of the "son of".
Finding out from the Ms what is up in the way that makes her the least defensive would be best for the kid (I think-) because if she feels a threat, she might not want to admit her mistake. You will find out more of the story as time goes on, but does your son need to go through that?
Perhaps (not from experience) I might suggest you use the first sentence, let her know your fear ("I'm afraid he's going to lose it at school and take his anger out on another kid" or whatever it is).
Rough night for you all. I hope you still get some good z's~
