A 30-year-old female was also injured, though not by gunfire, according to the Los Angeles Fire Department.
There are two shooting victims reported so far, with a 15-year-old boy suffering a critical head wound, and a 15-year-old girl was shot in the wrist and is said to be in a fair condition.
"We know this a very traumatic incident for all the children involved, particularly inside that classroom", said Steven Zipperman, chief of the Los Angeles school system police department.
Cops got a call to Sal Castro Middle School in the city's Westlake District just before 9 a.m. local time, a Los Angeles Police Department spokesman told local news channel KTLA.
"The school has been declared safe at this point".
Footage from the scene showed police vehicles surrounding the school's campus. An 11-year-old boy and a 12-year-old girl were grazed and were treated and released from the hospital.
As The Associated Press explains, district policy dictates that "students at middle and high schools in Los Angeles are subject to daily random searches for weapons using metal-detector wands, but officials have not said whether any such screenings occurred at the school Thursday".
"I'm just hoping it has nothing to do with him", she said.
Parent Claudia Anzueto, 41, said her 12-year-old son was crying when he used someone else's cellphone to call her.