Bridget McGuiggan, the school district's community relations coordinator, said the science classroom also suffered some water damage.
McGuiggan said students who use the damaged classroom will be moved to another room, but school will otherwise continue as normal.
Orland Park police say the bus driver believes a mechanical failure caused her to lose control of her bus, drive onto the sidewalk, through the grass, and into the side of the building.
People were inside the school at the time for after-school activities.
Police said an exterior wall of the school was damaged. The building will be tested for structural damage.
Police traffic investigators are looking into the crash.