This was formed in 1912 and aims to provide support for the school and a continuing link for past students throughout New Zealand, the Pacific and indeed throughout the world.

The OBA has, through the years, contributed freely of its time, energy and finance to provide many fine buildings and amenities for the benefit of students, thus enhancing the school. These improvements include the Memorial Gates, the Memorial Music Block, Swimming Pool Complex, Gymnasium, and Gully Pavilion, plus many other forms of assistance including an annual grant to the Headmaster’s Fund, disbursed at the discretion of the headmaster, for the benefit of all students.

The OBA over the years has organised many major functions; the 50th, 75th, 85th, Centennial and 110th Jubilees, in addition to many other pleasant social functions within the school and throughout the country. These sometimes coincide with major school fixtures in Wellington, Hamilton, Auckland, Palmerston North, and New Plymouth.