School are really anti any end of year party. They discourage kids and parents who might try to organise one by not letting any discussions/tickets/money be on school premises.
They say it's because 16 year olds will drink and cause mischief. Well surely all the other schools in the county would have the same issue and secondly 'thanks for the faith in your pupils!'.
I know 'Proms' aren't everyone's cup of tea, but it is a lovely way to end your GCSE's. They don't have one at the end of sixth form either, in case you wondered.