The Salt Lake Tribune reports the Granite School District in the Salt Lake City area obtained the weapons from a U.S. Department of Defense program that gives surplus equipment to police agencies.
There are 62 agencies in Utah that get equipment from the program, but Granite is the only one whose primary responsibility is schools.
The school district's police officers don't keep the rifles with them at all times. They are locked in a rack inside their cars.
It's unknown how many other school districts in the country have received rifles from the program, but there's at least one in California.