The event took place Friday, Jan. 12, when the teen attacked a staff member with a weapon, said Hastings-on-Hudson Police Lt. David Dosin.
During the altercation, another student tried to intervene and suffered a "superficial" stab wound to the chest and a laceration to the hand, Dosin said.
The staff member received an injured lip, he added.
The 13-year-old, whose name wasn't released because of her age, was charged with two counts of felony assault and criminal possession of a weapon, Dosin said.
Her case will be handled in family court due to her age.
Graham Windham is a New York City-based nonprofit that runs residential treatment centers and schools throughout the area for children, youth, and families affected by abuse, neglect, and delinquency, with needed services.
Click here to follow Daily Voice Chappaqua and receive free news updates.