Teaching: they are doing it wrong... The only thing those schools are teaching their students is that education is less important than a concert of a boy they won't even like in a few years, whereas at school they are studying for their future
They should have told those kids the exams WILL be in the week of the concert and they will NOT be able to attend or they would fail at school. This would have been more educational, as they'd learn their material + the life lesson that you cannot always have what you want. You have responsibilities to yourself and to others and when you get a job you cannot take just any day off to go to some concert, you can only go if your schedule and boss allow you to.
I'd refuse to reschedule my exams if I were their teacher, if they wouldn't show because of the concert I'd have them fail it automatically.....