Dr. Holbrook's Military School was a military academy and boarding school for boys located on Briar Cliff, which overlooked the Hudson River near Sing Sing (now Ossining), New York.
Holbrook's was founded in 1866 by Reverend D. A. Holbrook, Ph.D. (died December 1898). In 1890, Dr. Holbrook's sons, Dudley Holbrook and Henry Holbrook, became involved with running the school; they were joined in 1899 by their brother Dwight Holbrook.
In 1903 the school consisted of six forms, the first two making up the Lower School and the remaining four making up the Upper School; in the Upper School students chose from three curicula, Classical, Latin-Scientific, or English-Scientific.
Students received grades for Deportment, Application, Spelling, Declamation and Composition, Church Attendance, and skill at Military Drill, as well as in classes like Arithmetic, Algebra, French, Latin, and Greek.
In 1903 the school grounds covered 24 acres (97,000 m2).
Holbrook's operated until at least the early 1900s.