The San Diego Unified School District's police department obtained the semiautomatic AR-15s in 2010, but school board President John Lee Evans said he didn't know about the arsenal until he read about it in a newspaper last month.
"I did not know these rifles existed in the district," Evans told U-T San Diego. "I don't know if policies have to be changed, but the school board and the public need to be informed as to why these are needed and how they will be used."
Officers have carried the rifles in public at least seven times during on-campus incidents in the city, the newspaper reported Saturday.
District officials said they were not legally required to get the board's approval to authorize the use of the AR-15s. U-T San Diego said officers underwent training in their use and had to pay for the rifles out of their own pockets due to chronically tight budgets.
So far, 17 of the district's 43 officers have obtained the weapons.