If you've been harbouring doubts about the boy with a beard and a bass voice, or the girl with middle-aged spread, then now is the time to act.
Here are a few tips on what to look out for when identifying an imposter or to use the latest jargon, a "Brandon", who may have illicitly entered your institution.
* At parents' evening you notice his parents are both octogenarians
* He drinks beer with his packed lunch
* In football matches he is very strong on the high ball
* His school uniform is too tight
* In the nativity play he is the most convincing Joseph you've ever seen.
Bear those things in mind. Keep your school Brandon-free.
Jeremy Davies is a former English teacher in south London.