So I guess a prom is a dance, for seniors?
Different high schools have different traditions but this is how it worked in my high school. I went to a very large public school and there were 2000 students and 4 grades (9, 10, 11, 12). There was a homecoming dance every fall, usually in October, that took place on the Saturday night of homecoming weekend. That was the weekend that most graduates were supposed to come back and cheer their football team and other sports, but very few did. This dance took place in the school cafeteria. You wore cocktail attire and dates usually went out to dinner tete-a-tete (in couples, not groups) before the dance. Students from all grades were allowed to attend. They could also bring a date from another school if they didn't want to go with someone from our school.
Prom was also a dance, generally in mid-May. But it was fancier. The attire was formal and it did not take place on the school grounds. A ballroom, event center, museum or country club was rented and decorated. I have heard that other schools have a separate Junior prom and Senior prom. At our school, it was one prom. You could be a Junior (grade 11) or Senior (grade 12). Juniors purchased tickets and Seniors got in free. In this way, it was said that the Juniors were hosting. If you invited someone, they could be just about any age and attend any school. At my school, it was still mostly couples. I didn't know people who went in groups, although, you didn't have to go with someone you were romantically involved with. I went with a different male friend each of my two prom years.
It was somewhat of a tradition to lose your virginity to your prom date and so some parents would organize something called "After Prom" which was a lot of fun and very informal. This took place after the prom dance. This was to encourage couples to go have fun at After Prom and not play scrabble at a motel, friend's house with parents who weren't around, or most often a large Cadillac. After Prom had bounce houses, fake casino games, decorations, music, etc.
For some students the night went like: 1) go to fancy restaurant with your date and maybe another couple or two, 2) drive a parent's car to Prom and dance 3) change out of your ball gown or tux into blue jeans and go to after prom 4) by then the sun was coming up and go have breakfast and then 5) head to your own homes.
For other students, the night went like: 1) go to fancy restaurant with your date, 2) drive in a rented limousine to prom and dance 3) leave early and find someplace to play scrabble 4) head to your own home and tell your parents that you went to after prom and had breakfast.
Our high school was very
cliquish. The social groups didn't tend to mingle. People from various groups tended to completely ignore people from other social groups. I don't even think they said "excuse me" if they needed to pass each other in the hallway or bathroom.