Pump Up the Volume

Pump Up the Volume. 1990 New Line Cinema.
Starring: Christian Slater, Samantha Mathis, Mimi Kennedy, Scott Paulin, Ahmet Zappa
Director: Allan Moyle
Buy Pump Up the Volume at Amazon.

Mark Hunter (Slater), a loner in his suburban Arizona high school, only comes alive every evening when he starts broadcasting his pirate radio station from a transmitter in his bedroom using the handle "Happy Harry Hard-On" as he rants about what's wrong with American society. Nora Diniro (Mathis) is intrigued enough by the nightly pirate radio broadcasts that she tracks down Mark. The show itself becomes more and more popular and influential among the students, to the point that it causes enough problems in town that the FCC is called in to investigate. Also, it is learned that the school principal has been expelling "problem students", especially ones with below average SAT scores, which becomes one of Mark's favorite topics.

Realizing that he's created a monster with his broadcasts, Mark takes it upon himself to stop it, broadcasting his final message as himself. As the movie ends, other students inspired by Mark take to the airwaves on their own pirate signals.