If you're not familiar with "Welcome Back, Kotter" here is the premise of the show from Wikipedia.
The show starred comedian Gabe Kaplan as the title character Gabe Kotter, a wise-cracking teacher who returns to his high school alma mater—the fictional James Buchanan High in Brooklyn, New York—to teach an often unruly group of remedial wiseguys known as the "Sweathogs." (The nickname reflected the fact that the remedial classes were held on the very top floor of the high school.)