Several thousand past students, teachers and hostel staff have passed through YAHS since it was opened in 1922. The Old Yanconians' Union, founded in 1929 in Sydney and comprising former students living and attending Hawkesbury Agricultural College or Sydney University and headed up by former principal, Ernest Breakwell, strove to keep those students actively interested and involved in their 'old school'.
Almost a century later, this involvement is a primary aim of the Old Yanconians' Union: active and financial involvement through working bees, the funding of specific projects, Gala Day, representation and support for the school.
The OYU seeks to contribute to school life in such a way that benefits current and future generations of students. Recent projects include: school War Memorial, removal of old gas boiler, provision of barbecue unit and front lawn seating, financing part of front ovals irrigation system and provision of exercise stations around the Giltinan Sports Hall.