Sergeant Beth Larson says firefighters first discovered the damage after responding to a fire alarm at the school on Yew Street Road.
She says at least two people broke into the school and discharged fire extinguishers all over the building, damaging several computers.
The vandals also splattered spray paint and other kinds of paint on the windows, walls and desks.
An estimate of the damage is not yet available.
Anyone with information about the vandalism is asked to call 9-1-1.