Back in my day (I'm only 38!) the 6th formers had a formal dinner in the local posh hotel I guess, but that was it. No expensive outfits, hairdo and make up, transport, pre party, after party etc.
I finished A levels in 1991. We only had a sixth form 'ball' - wasn't called a Prom then - not a GCSE one. Was at local 'nice' venue with a sit down meal and a disco after.
Everyone did get properly dressed up though and most girls had hair and make up done. There were no limos, etc though - mind, there was no limos at DD's either despite being an independent school where some people do have a lot of cash flying around. Mine was just your average comp, in a not overly great area, certainly not a wealthy area. All our local schools had sixth form ones.
I admit to being really sceptical about the whole GCSE Prom idea before we were thrust into the whole GCSE year, and actually it was lovely. DD worked really hard over her revision - way more than I (or dh) ever seemed to for GCSEs or even A Levels. She was really excited to partying with her friends.
And it wasn't really OTT compared to many - there was a meal and a disco, there were nice dresses (though most were not crazy money; you can get a nice looking prom dress for about £20 on ASOS, as well as dearer ones) and most had hair and make up done either at a MAC type counter, at a solon or, the more 'make up' able of them, at home. The boys were looking smart in either lounge or dinner suits.
But there wasn't any unpleasant competitiveness, there was no ostentatious flashing of cash, there were no fancy meds of transport there and back and even the so-called after parties ended up fading to nothing, with most people just going back with friends with just 4 or 5 of them at each house (mostly due to pick up distance and sharing lifts.) There was no having to have a date for the night or any of that pressure either - almost all juts went with the mates.
So, I have slightly changed my mind on them. It was lovely and so long as not OTT I think they can be quite sweet events.