I wasn't actually suggesting that your granddaughter's school should have had a prom (with parents forced to fork out hundreds of pounds for dresses and transport).
Indeed, I welcome the fact that they went down a far more traditional route. (I regard it as ridiculous that primary school kids should have proms. Also, having taught kids who couldn't even afford a cheap ball-point pen for school, I do worry that many secondary leavers will end up excluded from their end-of-school activities through the 'Americanisation' of the whole thing).
I don't remember anything special when I left either primary or secondary school. We simply walked out of the door and that was it. Later, when I was teaching at secondary level, we abandoned end-of-school discos because we knew that nearly all of the kids would get blind drunk, knowing that there was absolutely nothing we could do about it.