Classes began during the fall of 1917 at the new campus, amid continued construction that helped shape much of the school's current appearance.

Poly Prep's most recent and dramatic expansion occurred in 1995, with its acquisition of the historic Hulbert Mansion from the Brooklyn Ethical Culture Society, a site formerly rented by the now defunct Woodward Park School.

The new property was converted into Poly's Lower School, offering classes for students from nursery through 4th grade.

In April 2009, Poly Prep's Lower School won the Lucy B. Moses Award from the New York Landmarks Conservancy as an outstanding example of historic preservation and renovation.

The allegations surfaced during Foglietta's first year at the school, during the tenure of Headmaster J. Folwell Scull, who was the head of Poly Prep from 1949 to 1970.

Poly Prep consists of three divisions, beginning with the Lower School located at 50 Prospect Park West in Brooklyn.

[citation needed] In the 107 years since the opening of the Dyker Heights campus in 1917, Poly has had six headmasters (currently known as Head of School): Joseph Dana Allen (1917–1949), J. Folwell Scull (1949–1970), William M. Williams (1970–2000), David Harman (2000–2016), Audrius Barzdukas (2016–2023), John Rankin - interim (2023-2025), and Noni Thomas López (2025 - TBD)