Hackley School is a private college preparatory school located in Tarrytown, New York and is a member of the Ivy Preparatory School League. Founded in 1899 by a wealthy philanthropist, Mrs. Caleb Brewster Hackley, 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 coeducational.