The incident happened around 12:45 p.m. in a classroom at Robert Stuart Middle School. The students fired the gun into a table leg.
Twin Falls police spokesperson Josh Palmer said it is likely that the single discharge was accidental. No one was injured.
Palmer said the gun was handed over to school district staff and police by the students. He added that the police was more focused on ensuring the safety of students and staff.
Palmer did not reveal what kind of gun was discharged. Along with the discharged gun, the police also found another gun in the 14-year-old student's bag. Officers say one of the firearms was stolen and another had an altered serial number.
The student is being held in the Snake River Juvenile Detention Center and is charged with: unlawful possession of a firearm, altering a serial number on a firearm, possessing a firearm on school property and unlawful discharge of a firearm.