Old Haileyburians Association | 176 followers on LinkedIn. OHA--est. 1903--is the alumni association of the largest school in the Southern Hemisphere, Haileybury College. | The Old Haileyburians Association (OHA)--established in 1903--is the alumni association of the largest school in the Southern Hemisphere, Haileybury College. Haileybury College has six campuses; five in Australia and one in China. OHA provides mentoring opportunities, networking opportunities, and clubs focused on sports, the arts and social justice.