The film follows six teenage high school seniors who hold a wounded police officer hostage and barricade themselves inside the school.
In an urban Queens high school students, Julius Zacharias 'Ziggy' Malone (Robert Ri'chard), Lester DeWitt (Usher Raymond), who lost his father, hard-working student Stephanie Williams (Rosario Dawson), criminal Rodney J. Templeton (Fredro Starr), rebellious pregnant Lynn Sabatini (Sara Gilbert), and Robert Tremont a.k.a. "Rivers" (Clifton Collins, Jr.), attend the history class of Ken Knowles (Judd Nelson). Police officer Dante Jackson (Forest Whitaker) tries to arrest Lester after a misunderstanding when the classroom's windows are broken by rocks, Mr. Knowles takes them to the principal's office, where Principal Allen Armstrong (Glynn Turman) tells Knowles to take them "anywhere".
Since there is no space anywhere in the school, Knowles and the kids go to a local diner, where a robbery takes place. Knowles confronts the robber, who was a former student that dropped out of school. Principal Armstrong is infuriated by what Knowles has done, and puts him on administrative leave. Lester, Stephanie and Ziggy are at the main office as Knowles leaves the school. Stephanie is disgusted that Principal Armstrong has ignored that he told Knowles to "take the class anywhere" and confronts him about this. In response Principal Armstrong suspends Rivers, Ziggy, Stephanie and Lester from the school and calls in Officer Jackson to remove all of them. Ziggy decides to leave but Officer Jackson restrains him. This event is witnessed by other students at the school and soon everything turns into a small riot.
Lester tries to resist Officer Jackson and loses, but Ziggy picks up Officer Jackson's dropped Glock 19 pistol and says "I [Ziggy] cannot go home." The reason for this, is because Ziggy has been physically abused by his father for many years. Officer Jackson tries to restrain Ziggy but gets accidentally shot in the leg as he grabs for his gun. Principal Armstrong tells school security to call an ambulance and the N.Y.P.D. in order to arrest Ziggy. Lester then grabs the gun and orders everyone to evacuate the school. This finally forces the N.Y.P.D. detectives to come in, led by Detective Audrey McDonald (Vanessa L. Williams) as a negotiator.
In the middle of all of this, there is a subplot in which Lynn berates Stephanie for being a "goody-two shoes", and a fight in the school's library that includes Rivers and Rodney, as well as Officer Jackson fleeing from Rodney and the others after knocking him out to use the bathroom. Another notable subplot was Ziggy showing everyone his artistic talents, such being a mural of himself and others on a classroom wall.
Still waiting after a couple of hours, the group continues to hold Officer Dante Jackson against his will. Lester tells everybody, including Stephanie and Dante about how his father (Robert Lee Minor) who was gunned down during a wrongful arrest. In the next few scenes, Rivers, Lynn, Rodney, Ziggy, Stephanie, and Lester, a.k.a. "The Lincoln 6", are all becoming infamous across New York City, as they are exposed and identified on such networks such as BET, VH1, NBC, NY1 and CBS, as well as MTV, as well being announced on radio. Debate continues as the events taking place, until Detective McDonald and her colleague (Vic Polizos) debate on getting the kids something, which after several hours of stalling, the electricity being shut down at the school and the SWAT team storming in on the others as Lester takes Officer Jackson on top of the roof. There, Lester tells Officer Jackson that he resents all policemen for what has happened to his father, and Jackson tries to reassure him. The confrontation goes horribly wrong when Ziggy comes to the roof and is shot down and killed by a sniper from a hovering police helicopter. In the end, 5 of the remaining surviving teens are taken into custody shortly after Ziggy is pronounced dead.
As the film reaches its climax, the narrator talks about what happened to the kids and the officer: Officer Jackson testified in court that the events did not happen as the media have portrayed them, thus giving the kids a less sentence. Lester spent two years in state prison and has gone off to a city college to study law. Stephanie spent one year in prison and went to study at St. John's University, Lynn was sentenced to one year in prison, but was released earlier due to having her baby boy (named after Ziggy) and is never heard from again. Rodney spends an unknown amount of time in prison and becomes a Muslim, Rivers is forced to join the military, due to the judge having him spent years in prison due to his priors or join the army. Mr. Knowles has been rehired back to the school and still teaches history. The end also shows Lester and Stephanie looking a painting that was crafted by Ziggy, who is forever remembered as the next Jean-Michel Basquiat a.k.a. "The Radiant Child".Usher Raymond as Lester Dewitt
Forest Whitaker as Officer Dante Jackson (In the movie, he wears the three blue stripes which identify a Sgt but is called officer)
Rosario Dawson as Stephanie Williams
Robert Richard as Zacharias 'Ziggy' Malone/The Narrator
Judd Nelson as Ken Knowles
Fredro Starr as Rodney J. Templeton
Sara Gilbert as Lynn Sabatini
Clifton Collins, Jr. as Robert 'Rivers' Tremont
Glynn Turman as Principal Allan Armstrong
Vic Polizos as Capt. Monroe
Vanessa L. Williams as Detective Audrey McDonald
Robert Lee Minor as Lester's father (flashback)
The film was mostly shot at Calumet Career Prep High School in Chicago, Illinois, although set in New York City.
A soundtrack containing hip hop and R&B music was released on November 9, 1999 by Yab Yum/Elektra Records. It peaked at #19 on the Billboard 200 and #4 on the Top R&B/Hip-Hop Albums.
Light It Up was released on November 10, 1999. At Metacritic, which assigns a normalized rating out of 100 to reviews from mainstream critics, the album received an average score of 43, which indicates "mixed or average" reviews, based on 27 reviews. The film received negative to mixed reviews from film critics, holding a rating of 38% on Rotten Tomatoes. Roger Ebert, said about Light it up, "The problem is the movie is too predictable--so predictable that it keeps it from truly generating suspense." However audience ratings give Light It Up a 75% like rating according to Rotten Tomatoes based on 6 thousand ratings.