The proper thing to do is to get everybody in the room. The kids, his parents, school faculty, etc
Speak evenly but firm as fukk.
Lay it all the fukk out like like this:
"Your son physically
and sexually assaulted my daughter and then he verbally threatened her. I'm not here for any explanations or apologies. I'm here to inform you what will happen going forward. Your son will never lay so much as a finger on my daughter ever again. It is up to you to communicate that to him. It is solely up to you to see to it that he never physically assaults my daughter again.
If this should happen again, everyone in this room, other than me and my daughter, is responsible. I will do
whatever is necessary to protect my daughter from physical violence and ensure that my daughter not only is safe, but feels safe while she exercises her right to pursue an education. There won't be any further discussion about this as I have made myself very clear today. Thank you for coming. I bid you all a good day."
Let your word be the first and the last.