Went to high school outside NYC. Junior prom in 1978, senior prom in 1979. It was called "the prom". Never heard it called "prom" outside of the movies.
Junior prom -- my parents were cheapskates when it came to me and wanted to find a way to discourage me from going to prom so they wouldn't have to spend money on me. (I was forbidden from getting a job at that time, so I had no money of my own.) So I was given $20 and 10 minutes to find a gown or I couldn't go. They were both upset when I managed to do that. Ha. (In contrast, my sister was given $500 for her prom gown. GUess you can tell who was their favorite.) It wasn't the greatest gown, not what I would have picked if I'd had more money or time, but it was okay -- cream colored sleeveless dress with a ruffle around the neckline in Qiana. Then they refused to give me any more money. My boyfriend's mother very sweetly bought me everything else (undergarment, shoes). My boyfriend wore a milk chocolate brown tux with dark brown velvet collar and trim. Senior prom I knew what to expect now, so I saved all my money from my birthday and Christmas and told them I was buying my own stuff. Which I did. Got a nice baby blue gown at the mall -- actually it was great with my coloring and my figure, so I'm still happy with it. Those pictures of me are some of the best ever, to be honest. My date wore a dark blue tux with, of course, a ruffled shirt.
Junior prom was the "less fancy" event and was held in March. Senior prom was held in May. Long dresses and tuxes, dinner included, dancing after dinner with a live band, plus voting for the queen and king. After senior prom, a few of the wealthier kids had after-parties because they were the only ones with big enough houses. The big thing was for the guy to borrow a "fancy" car -- like a Trans Am or Mustang -- from an older brother or uncle. Girls generally, but not always, had their hair done. I didn't know anyone who had their nails done. 99% of the girls got their gowns at the mall, leading to five girls in the same gown at my senior prom -- luckily, all but one of them thought it was a riot. Had a great time at both proms. It was the disco era, so everyone was dancing. Tons of fun. Both of them were couples only -- no single tickets could be bought, so no singles or groups.
The prom here (Midwest) is very different. It's called "prom" and there is only one -- for junior year. BIG expensive gowns, BIG hair, nails, limos, limos, a "promenade" and no dinner, just dancing for 2 hours. So basically prom was 2 hours. All of that prep for 2 hours. What a waste, IMO, but I went ahead and put a smile on my face as we shopped, got her hair done, etc. In the end, my dd thought it was a big build up and then nothing once you actually got there. She says the best part of the whole "prom business" was shopping for her gown; the rest she could have done without. Just a big letdown. She says now she doesn't know if she went back in time, if she'd bother with it.
But I don't know how much of the difference is due to geography or time. Weddings are much more crazy then they were when I got married, so it's not a surprise to me that proms are also much more crazy.