Darlington was the third seed for the team.
He has been playing squash for the last seven years and, like Matthews, got into the sport thanks to family involvement.
"Mum and dad played squash, and I've just grown up around it," he said.
He was excited to be part of the national squad but was nervous during the announcement of the team, as Matthews got called up before him.
"I was like, come on, and then I heard Cullinane College, and then I was like 'yes, I got in'."
The New Zealand team will travel to Queensland in two weeks from now to take part in the trans-Tasman tournament, where they will play against teams from states across Australia.
Darlington said he hoped to have fun at the tournament, and he was going to treat it as a learning opportunity.
"Just to see what they've got over there and the difference between Aussie and New Zealand, what they do differently, and maybe incorporate that into my game," he said.
Matthews and Darlington are the only two Whanganui athletes in the team.
This year was the first time Cullinane College had sent a squash team to the nationals, and assistant dean Simon Peterson said the school was very proud to have two students make the national squad.
"To get two students really pushing the levels of sport, to get that high, is amazing from our perspective, and we couldn't be more proud."
