Hackley School is a private college preparatory school locate in Tarrytown, New York and is a member of the Ivy Preparatory School League. Founded in 1899 by wealthy philanthropist Mrs. Caleb Brewster, Hackley was intended to be a Unitarian alternative to the mostly Episcopal boarding schools throughout the Northeast. Since its founding, Hackley has dropped its sectarian affiliations and changed from all-boys to coed. Hackley is divided into three schools on the same campus: The Lower School, The Middle School, and The Upper School.