My son is in Year 12 and tells me that in a lesson today the grades of the Year 13s who are studying the same subject were put on the board by the teacher. He could see how each named student was doing under each topic (e.g they were in an English lit and could see the Year 13 french grades broken down into topics, i.e. poetry, Shakespeare, modern text, 19th Century text etc).
He says it was on the board for a good few minutes; enough for him to tell me how well (and not well in some cases) some of our friends kids are doing in that subject. No comment was made about why it was put up there or anything, so he thinks it was put up in error and the teacher didn't realise they'd put it up.
Is this a GDPR breach, and if so what (if anything) should he or I do about it?