Karla told Fair Go she always wore trousers outside school, and decided to wear them to school after being sick with a cold. She chose straight black trousers - similar to those worn by the male students - saying they were warmer and more comfortable.
"I was so much warmer, I could move freely. It was just so much easier," she said.
But her decision fell foul of school rules and Karla was sent home to change to the regulation girl's skirt.
Karla said making girls wear skirts was "following the rules from the 1950s".
"We should be catching up with the times and not living in the past.
"Most women you see walk down the street wear pants or shorts, not skirts."
She has taken her clothing rebellion to social media and has received a lot of support as well as some criticism.
McAllen said the uniform would be reviewed by the school board this term.
"The board believes that the policy has been in place for many years and does not adequately cater for all student needs. An important part of the review will be seeking feedback from all students and their whanau."
McAllen said the review would be finished in time for the next academic year.
He said the school was "concerned" that Karla went to Fair Go rather than approaching him or the school board.
"We strongly encourage diverse open dialogue on matters that are of interest and impact on our student body or their whanau."
The Whanganui Chronicle asked other principals whether they planned to review uniform policies.
Peter Kaua from Whanganui City College said there was no plan to review their school uniform.
"We haven't had a need for it."
He said female students who were part of the school's military academy wore trousers on parade.
"They're the only female students in our school who wear trousers."
However, Cullinane College is conducting a regular review of rules and procedures, and acting prinicpal Marty Bullock said that would include uniforms.
He said the board of trustees, which included a student representative as well as representatives of the Catholic Church, would do the review.
"Any change will take a while to be worked through."
Tania King, principal of Whanganui Girls' College, declined to comment.
