Georgia Johnstone, Kristal Roberts and Alannah Smyth (all 18), were named joint duxes - the first time three pupils have shared the honour since the school started the award 27 years ago.
''This wasn't something we'd do lightly, but they're all achieving excellence in their respective subjects and there was no way we could single out one or even two,'' principal Mason Stretch said.
Mr Stretch said it was a ''very academic year 13 class this year'' and the winners were ''three fully deserving young women, all very astute, committed and well-grounded, achieving at a high level.''
Georgia said the duxes were ''blown away'' by the announcement at the college prizegiving.
Kristal said the trio ''kind of knew we were in the running, but never thought all three would win it''.
The number of year 13 pupils, 65, was a relatively small group so they all knew each other well, Alannah said.
''It was a real surprise to everyone, though, when they said there would be three duxes and then read out the names.''
Georgia plans to study at the University of Otago next year for a bachelor of science degree, majoring in genetics.
She hopes to build a career as a genetic counsellor.
Outside school hours she is a keen netballer.
Kristal will head to Massey University in Wellington to study for a bachelor of design degree.
Earlier this month, she won the Cromwell Sports Person of the Year supreme award for her achievements in slope-style snowboarding, which included being selected for the Winter Games in Queenstown.
Alannah will study law at the University of Canterbury and her goal is to end up in international law, perhaps focusing on human rights for the United Nations.
She enjoys playing hockey and is a member of the Air Training Corps.
