Deputies from the Los Angeles County Sheriff's Office rushed to Highland High School in Palmdale just after 7 a.m. local time Friday morning after receiving calls of shots fired in the building.
The sheriff's office said one person, a student at the school, has been detained. He was described as a 14-year-old of Hispanic descent. His name was not immediately released. A rifle was also recovered.
The victim, also 14, was shot in the arm and is listed in stable condition at a hospital, authorities said.
The Bureau of Alcohol, Tobacco, Firearms and Explosives has also responded to the scene.
About a half hour after the Highland calls, gunshots were reported at the Manzanita Elementary School, located about seven miles away from Highland High School. Deputies searched the scene and found the report to be unfounded.