City police said the seventh-grade and an eighth-grade boys were being held pending formal charges, The (New Orleans) Times-Picayune reported. The weapon was found in the ceiling of a boys restroom during the morning, the newspaper said.
The school was locked down for about 2 hours while police and K-9 dogs searched the school any other weapons. None was found, the newspaper said.
City police Lt. Gerald Sticker said investigators had yet to determine who brought the gun into the school and why.
St. Tammany Parish school district spokeswoman Meredith Mendez said an automated "robo call" went out to parents to let them know what was going on.
The lockdown was lifted at around 10 a.m., and students were released to their waiting parents, the newspaper said.