BALDWIN PARK, Calif.—Officials say a 15-year-old student has been arrested at a high school east of Los Angeles for carrying ammunition on school grounds, and a handgun of the same caliber was later found at his home.

The Baldwin Park Unified School District said in a statement that administrators at Baldwin Park High School received an anonymous tip that a student had brought a gun to campus. School district police found the boy with a .40-caliber magazine containing 10 rounds of ammunition, but no gun.

Officers were allowed to search the boy's home and there found a .40-caliber handgun.

The boy's name was not released and it was not immediately clear what charges he could face.