Not from the UK -- proms exists here; and attending it
twice; during K to 10 era: one at 2nd year high school (equivalent to grade 8/9, around ages 14~) and one at 2nd year college level (equivalent to grade 12, around ages 18~ or less).
It can happen at the same time, in between those years or not. Depending at the school.
I did attended both times.
And literally did nothing.
I just fell asleep on it.
With whatever fancy dress and shoes I've been wearing, in a middle of whatever music and lights that was being blasted at the time.
At those times, I've talked to no one and just slept on whatever table I was assigned, ate, then leave.
Too bad I won a raffle prizes but I wasn't there to receive it.
I'm also not from the UK (I'm a Yank). My high school (which was years 9 through 12) had a policy where anyone in year 11 or 12 could go to prom. And anyone with a date in years 11 or 12 could go too. Some students went every year. I never went.
My school even let alumni attend the prom, provided we had a date in years 11 or 12 (and provided we were below 21 years of age). My first year out of high school, I *kinda* had a chance to attend prom. I chickened out.