Twelve months ago Auckland schoolgirl Kayla Cullen did not even consider herself having a chance of making the New Zealand Under-21 side for the World Youth Cup.

The 17-year-old shooter had just received her first call-up to the Under-21 squad for last year's tour to Australia, but given some of the other names in the programme she was pretty sure she didn't have a shot of making the final 12 for the world tournament.

Then, when she suffered a serious knee injury on that tour, Cullen thought her chances were well and truly scuppered.

Luckily for her, New Zealand Under-21 coach Yvette McCausland-Durie wasn't so quick to write off the talented teen.

The national selectors kept in regular contact with Cullen as she underwent rehabilitation after surgery on a ruptured anterior cruciate ligament and were blown away with the youngster's performance in her first game back in the New Zealand Secondary Schools trials in Christchurch last month.

Cullen was swiftly rewarded with not only selection in the schoolgirls team, but also invited to trial for the national Under-21 side this week, where she once again impressed.

Still, Cullen said she was shocked when she got the call from McCausland-Durie on Thursday morning, telling her the good news.

"I wasn't expecting it at all. I was really surprised when they called me in to trial," said Cullen, who seems rather bemused at all the attention she is getting over her selection.

The New Zealand Under-21s will attempt to defend the World Youth Cup in the Cook Islands in August, and Cullen said the team had a pretty stern challenge ahead of them with the well-prepared Australian side the big favourites.

"I'm really nervous, but excited," the Auckland Girls' Grammar student said.

"The level is such a big step-up from secondary schools.

"You have to put in a lot more work in fitness and that sort of thing so I've got quite a way to go yet."

McCausland-Durie said what set Cullen apart from the other triallists was her speed, movement and timing.

The slightly built 1.8m shooter is also an impressive athlete, competing at national secondary schools level in the 100m sprint and long-jump.

"I think people will see her as quite an exciting talent. She plays at both goal shoot and goal attack, and offers quite a bit of mobility," said McCausland-Durie.

"It wasn't just about how well she did in relation to some others, but also about how well she fitted into the team and the game plan of playing that short flat ball so we can beat some of those long lankys that we're about to come up against."

But the New Zealand Under-21 coach said Cullen still had a way to go with her rehab before she was ready to take on the world.

"What happens over these next 12 weeks is critical.

"The challenge for us now is to get her well-conditioned and playing at the intensity required at that level," said McCausland-Durie.