The teenage boy was shot in the head and was in stable but critical condition at an area hospital.
The middle school and Belmont High School, which shares the campus, were placed on lockdown as police search the school, though authorities say there are "no outstanding suspects".
Three other individuals suffered non-gunshot injuries, such as minor scrapes.
Gloria Echeverria was outside a line of police tape preventing people from approaching the school, waiting for news about her 13-year-old son.
A 15-year old boy was shot in the head and critically injured and a 15-year old girl was shot in the wrist, her injures are not believed to have life threatening. Officer Madison said that the motive was unknown.
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It all comes down to metabolism, the rate at which the bears use energy, according to Anthony Pagano, a PhD candidate at U.C. All over the Arctic , scientists have seen evidence of weakened polar bears, Pagano said.
Doctors say the most seriously injured victim of a Los Angeles middle school shooting has a good medical prognosis.
After the campus was declared safe Thursday, the school day continued, and students could talk to counselors about the shooting, said Vivian Ekchian, interim superintendent of the Los Angeles Unified School District. Parents who wished to pick up their children early were directed to a baseball field near the school at Loma Drive and Crown Hill Avenue.
Officers could be seen leading a handcuffed girl to a waiting squad auto in news footage shot from a helicopter.
Students and teachers also consider the event was unintentional, some even saying the girl brought the gun to show it to her colleagues and not to do something wrong with it. "I had the gun in my backpack and I didn't know it was loaded and my backpack fell and the gun went off, '" he said. He also said that after the incident, he learned that his daughter was bullied at school. Even more, some of the students thought the gun was a toy.
One of the parents spoke to CBS San Francisco and said that she was anxious about her 13-year old son as the authorities did not allow the parents to approach the school after the incident.