Matthew, who attends Pompallier Catholic College, also wondered if he stood a chance. "I was honestly astounded," he said.
Every second year about 60 students are selected through nationwide auditions to join the choir for a two-year cycle.
They meet during school holidays for intensive rehearsals and public performances.
At the end of that the choir will plan to attend an international festival or competition.
Phoebe said she was most excited about meeting others who were passionate about performing.
"I just like singing and I like the musical theatre part of it."
Whangarei Girls' High School head of music Nicholas Grew said Phoebe was a fantastic student.
"I was surprised and not surprised she got in."
Matthew said being accepted into the choir was a bit scary as he had only ever sung in his school's choir before.
"I'm honestly not sure what to expect."
Like most teenagers, Matthew said he did not practise his craft as much as he should though he planned to change that.
Matthew also played three types of recorder, alto saxophone, clarinet, handbells and piano.
Matthew's father, Nigel Brereton, said it was a fantastic opportunity for his son.
"Who knows where it will end?"
While the two students both went to Maunu Primary School they had since gone their separate ways, but said it would be nice to have a friendly Northland face in the choir.
The last student from a Northland school to be accepted into the New Zealand Secondary Students' Choir was Gregory Burgoyne of Kerikeri High School in 2003-2004.
