The 14-year-old is considered a juvenile under the law so his name is not being released publicly.
The boy made his first court appearance Monday afternoon in Bloomington, where the state filed 16 felony charges against him.
They include discharging a firearm, unlawful restraint, unlawful possession and aggravated unlawful restraint.
Prosecutors argue the boy stuffed two Ruger pistols, a Beretta pistol, a fixed blade knife, a dangerous folding knife and a hatchet in his backpack and brought them to school Friday.
He's accused of firing one of the guns more than once at the ceiling a shortly after 8 a.m. during health class and refusing to let some people leave the room.
It's unclear if the state will try the boy as an adult. That decision is being considered, according to McLean County Assistant State's Attorney Bill Workman.
Workman also refused to elaborate about how exactly the boy got access to the arsenal of weapons, but did say he "had access to them."
A trial date is set for October 1. The teen entered a plea of not guilty and is being represented by a public defender.
He is expected to receive a psychological exam.
Possible penalties include probation, transfer of guardianship, time in a detention center or time in the state's corrections system for juveniles.