Lincoln High School in Queens in literally falling apart. With no money to fix the myriad of problems facing it, the students are forced to attend freezing cold classes in leaky rooms. When Ken Knowles (JUDD NELSON) takes his class "off campus" to find a suitable place for learning, Principal Armstrong (GLYNN TURMAN) decides to suspend him despite being the one who told the teacher to find any place to hold the class.
Knowles' students, including Stephanie Williams (ROSARIO DAWSON), the brightest one who can't wait to get a better education, and Lester Dewitt (USHER RAYMOND), whose academic and athletic prowess has suffered ever since police shot his father several weeks earlier, protest the decision. When things begin to get out of control, Armstrong calls new security guard and current city cop, Officer Dante Jackson (FOREST WHITAKER), to handle the situation.
When Armstrong announces that Stephanie, Lester and his good friend and talented artist, Zacharias "Ziggy" Malone (ROBERT RI'CHARD), will be suspended and sent home for their actions, Ziggy freaks out, prompting Jackson to attempt to restrain both him and Lester. As a result, Jackson's firearm is accidentally shot, hitting the officer in the leg.
Realizing things will only get worse if they give in, Lester grabs Jackson's gun and takes the officer hostage, ordering most everyone else out of the school. Those staying include Ziggy and Stephanie, who decides she has to attend to Jackson's wound, as well as Robert "Rivers" Tremont (CLIFTON COLLINS, JR.), the school hustler who witnessed what transpired.
Joining them is Rodney J. Templeton (FREDRO STARR) the tough school thug who's trying to avoid some gangsters waiting outside for him, and Lynn Sabitini (SARA GILBERT), an angry and caustic teen who's just learned that she's pregnant.
As the police and SWAT teams arrive and surround the school, Lester and the others try to figure out what to do while Jackson tries to convince them to stop their insanity lest they face far more serious problems. With police negotiator Audrey McDonald (VANESSA L. WILLIAMS) racing against time to prevent the gung ho police from storming the barricaded library, the small group of students hopes that they and their demands for a better school are taken seriously.