The 1978 movie Grease is based on the 1971 stage musical of the same name and is set at and around Rydell High School in 1958. I'm not going to get into too much detail about the plot... chances are you know it, and it's not exactly complicated anyway. Good girl Sandy meets bad boy Danny during the summer and they become infatuated with each other (Summer Nights); I'm not going to insult your intelligence by saying they fall in love, because these two idiots don't have a clue what that is. Then- surprise- Sandy ends up attending her senior year at Rydell, where Danny also goes to school. Afraid that he will appear uncool in front of his fellow greasers if it becomes known he's gaga over a goody-goody like Sandy, Danny acts like a jerk to her (is it an act though, or is he merely reverting to his true form?). This causes her to assume that he doesn't care about her... cue the tears and sad songs (Hopelessly Devoted To You) and lots of angst as Danny tries to win her back (Sandy). There's a subplot about skanky Rizzo and male skank Kernickie having a pregnancy scare, and also a drag race which exudes whatever the opposite of suspense is (Greased Lightening), and then of course it all resolves in the end in a song & dance scene (You're The One That I Want). Please understand that I'm not knocking song & dance as a staple of musicals: there are plenty that I love. This just isn't one of them.
Also- and this isn't unique to Grease; plenty of other movies/musicals have the same problem (Rent)- the "high school students" are anything but... most of the actors in Grease are in their late 20's and 30's, and it shows. In fact, several of them had to be shot in soft focus to hide their crows feet. I mean, really- do these look like any teens that you've ever seen?
In conclusion, Grease is not a good movie, its values are completely skewed, and John Travolta's affected mannerisms- and falsetto- just don't do it for me. Also, don't let the kids watch it.