I've been pondering this for far too long.
I have somewhat vague recollection of a book I read and loved as a pre teen. It was very dated even then - in fact I think it may have been my mum's from her childhood.
All I can remember of it is one chapter towards the end where the main character (female) has to sit an exam (I think for teacher training college but could be wrong). She's got some tablets which she thinks are painkillers and takes a couple as she's feeling ill - and when she gets into the exam it becomes apparent she has taken sleeping tablets by mistake.
A friend helps her cheat somehow - but afterwards they realise that there were different examination papers and theirs weren't the same.
I know this is a crap, vague description. Hoping that someone might help though!