The vote was largely ceremonial, as the 14 AR-15 assault rifles were ordered last fall, well before the Sandy Hook school massacre.
The rifles cost the district nearly $20,000 and are stored in locked safes on school campuses.
Critics say the assault rifles don't belong around schools, and the money should have been spent to restore counseling programs.
District police say there's no specific threat to the Fontana Unified School District. The board vote was unanimous.
