Character mistake: When Frenchie is the only person remaining in the soda shop a guardian comes on and starts singing a song. While he is singing the song (toward the end of his singing) all the girls scatteringly head back toward the stairs. While they are walking up, one of the girls trips over her high heels. It is clearly shown, she's toward the front going around the back of the seat Frenchie is sitting in, around the round thing.
Other mistake: This mistake occurs during the dance sequence 'You're the One that I Want.' John Travolta and Olivia Newton-John have just emerged from a 'Shake Shack' and are now ascending a ramp. For the lyrics ,Hoo hoo hoo... honey,' the camera zooms in close to their faces. You can see that the dance move is for the two actors to bob their heads close to each other's so that they nearly touch. They do it right the first time, but the second time they visibly mess up. John Travolta seems to try to fix his mistake, but Olivia Newton-John appears to crack up and leave the frame.
Continuity mistake: At the dance, when Frenchy insults Cha-Cha by saying, "With the worst reputation", Cha-Cha is shown (in the close-up) first looking at Kenickie, then turning her head around to give Frenchy a dirty look. In the next shot when Danny and Sandy are leaving the group, Cha-Cha is suddenly back at looking at Kenickie, then proceeds to give Frenchy the same dirty look again.
Visible crew/equipment: In the scene during the American bandstand, at the end of the song when the teacher is dancing in front of the band members, the crews can be seen. The dressing and the hair doesn't match Grease era at all, and someone is sitting on a director's chair as well. (01:06:20)
Continuity mistake: When Patti gets her skirt lifted up at the dance contest, the two boys who were dancing on either side of her in the previous shot have both disappeared.
Continuity mistake: When Danny and Cha-Cha are dancing to 'Born to Hand Jive', watch the position of Principal McGee. During the song, you can see her in the crowd. A few shots later, she is now standing near the stage on her own, and when we return to Danny and Cha-Cha dancing, you can see the Principal back in the crowd again.
Continuity mistake: On the first day of school during lunch, at one point Frenchie has out a small compact and is checking for food in her teeth. But when it cuts to a wider angle, suddenly the compact is gone, and she's looking over her shoulder.
Continuity mistake: There are red and white puffy paper decorations on each side of the door entering the gym for the dance-off. However, within a few seconds, the decorations on the left side completely disappear.
Continuity mistake: When the girls are all sitting in the outside cafeteria just before Patty Simcox comes over watch Marty. When Patty approaches she is lifting her fork to her mouth but when the shot changes she is holding out her hand to get Patty's card without having enough time to put her fork down in between.
Continuity mistake: At the beginning of the National Bandstand scene you see people filling the hat of the big "Rydell Ranger" figure with pieces of paper. During the next ten minutes the figure is often visible in the background and the hat is empty - nobody emptied it. After those ten minutes the hat has paper again and is then emptied. (00:59:00)
Continuity mistake: At the dance contest when principal McGee asks for applause for the committee who decorated the hall, someone replies "lets hear it for the toilet paper" and Eugene changes position during the following shots.