Madison police said a 17-year-old La Follette High School student was caught with a realistic-looking BB gun in his backpack on Monday.
The student told police he found the gun at a bus stop Monday morning and put it in his backpack.
Police said they also found six hallow cartridges that looked similar to brass bullets in the cylinder part of the revolver.
The teen was cited for bringing a dangerous weapon other than a firearm on school property.
Police said no one was threatened with the gun and it was not removed from the bag until it was inspected by a police officer.