According to officials, units were dispatched to the McDonough School at 111 Hillside Avenue on a report of a recovered CO2 BB gun.
Authorities said the firearm was located by school staff in an abandoned backpack in a classroom.
Officers later determined that it belonged to an 11-year-old student.
At this time, an investigation focused on two students is ongoing.
Police said that charges on at least one student are pending.