Los Angeles County prosecutors charged the boy on Thursday and want him tried as an adult.
His name wasn't released because of his age.
District attorney's spokeswoman Jane Robison says the teenager could face up to seven years in state prison if he's convicted as an adult of bringing a gun to a school zone, and discharging it in a school zone.
The maximum for a juvenile conviction would be nine months in detention.
The boy was arrested at Gardena High School after the incident Tuesday. Police say a gun he smuggled in a backpack went off and a single bullet wounded two 15-year-olds.
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