It's student-teacher week. Mr. Belding and Zack switch places. Kelly is Slater's History teacher, but Slater thinks she's being too serious about it. When she gives the class a test and everyone skips out on it, Zack faces a hard decision: to be their friend or their leader.

During a project for TV ads, Screech comes up with a new flavor of sauce, but the gang might go out of business when Screech becomes the target of a snobbish girl.

As the senior prom approaches, Zack discovers he still has feelings for Kelly. However, she already has a date, and Zack resorts to skulduggery to win her hand, while romance brews elsewhere.

As graduation approaches, Zack learns that he is just one credit short of graduating. Desperate to get extra credit, he joins Bayside's ballet company, and when illness strikes some of the other cast members, he calls on the gang for help.