We had the meeting with the principal yesterday. Peter was still home so he got to get the information firsthand instead of filtered through me for a change.
Overall she's prepared to keep him at the school (actually she said she would prefer that he stayed) but if we have another incident this term (only two weeks left) his school year would be regarded as finished. He is welcome to come back next year but there has to be significant changes in his behaviour or they will have no choice but to 'exclude him from the school'. If he has an incident at any time in the next semester, he's out.
I've had a chat with him about the results (he wasn't allowed into the meeting) and he has to see both the principal and vice-principal next Monday when he goes back to school. Here's hoping something sinks in!