Ghoul School (1990)

"Where the uneducated meet the undead."

Two sniveling high school dropouts plot to rob the school janitor and accidentally release toxic chemicals into the school's water supply. The swimming team are the first ones to turn into green-faced flesh-eating zombies, and they promptly go after the rest of the present school populace: two horror movie nerds, the members of a metal band and the world's worst basketball team.