Gabriel Kotter returns to Brooklyn to teach history at the very high school from which he graduated ten years prior. When the "Sweathogs" (a nickname earned by the underachieving students of Buchanan High) give him a hard time, Mr. Kotter fires back with his own unending wit, and before long, they accept him as one of their own. In return, he is able to teach these students to excel in ways they never thought possible.

The 1978-79 season saw the departures of Gabe Kaplan (although he would still come every few episodes) and John Travolta, so a new Sweathog by the name of Beau De LaBarre (Stephen Shortridge) was brought in.