"What astonished me was the fact rowing was something he should never have been capable of. Yet he treated his disability like other kids might treat acne - you get on with it. We've never spoken about it and it's a credit to Thomas that he's only ever been treated like anyone else. He never backed down and his motor skills have improved.
"He struggles on the power side of things as a smaller guy [1.82m, 64kg] but his power-to-weight ratio is as good as the best guy on the crew."
Dunn's determination intensified when he responded to an initial advertisement in the school notices.
"I went into the meeting and some guys laughed at me. They said I'd never be able to do it but a lot of those who laughed only lasted a couple of weeks - I'm still here. I don't think the laughs were meant in a nasty way, it was just an acknowledgment 'you'll never be able to do this, it's for stronger people'. That's what drove me."
Dunn leads a normal life in most respects but was told he'd never play sport.
His mother, Louella, says Thomas found it hard making muscular progress on the rowing machine because his muscles weren't as co-ordinated as a normal boy of 15. He had to concentrate hard but has reaped the rewards.
"It has completely changed his teenage years," she says."He loves the sport, is physically fit and feels included. It probably helps that he has been in a crew that wins."
Dunn's foray into rowing has fired his ambition. He's branched into sculling and has dreams of representing New Zealand in the adaptive sculls.
"I like challenging myself. I never want to let my disability stop me."