Police said the student brought the handgun for "show and tell" and allegedly tried to sell the weapon.
Multiple classmates said they took action, with one putting the student in a chokehold while several others tackled him and wrestled the gun away from him.
"I grabbed him by his legs and I pulled him down," said Dominic Carrillo, a La Habra High School senior. "I kind of just tried to hold him down. About three other of my friends hopped on top of him to try and hold him stable. And by then he was kind of flipped around and he said, 'Grab his gun.'"
The 14-year-old student was detained by police.
Investigators described the gun as small and said it was not loaded.