Karla took her case to TV's Fair Go when in July she was sent home from school because she wore trousers to school in violation of the uniform policy.
"Most women you see walk down the street wear pants or shorts, not skirts," she told the show. "We should be catching up with the times and not living in the past," she said, arguing that making girls wear skirts was "following the rules from the 1950s".
After Karla's case gained national publicity the school surveyed parents and students, asking for their suggestions for the uniform.
It set up a uniform committee, made up of students, staff and members of the board of trustees, who went through the survey responses and reported to the senior management and the board of trustees.
Mr Southee said there were a number of changes to the uniform for next year.
Of most note is that all girls and junior boys will now be allowed to wear black trousers as part of their winter uniform. The trousers are optional - girls may still wear the tartan skirt, and the junior boys grey shorts, if they wish. Girls must still wear skirts as part of the summer uniform.
Senior boys already wear trousers as part of their winter uniform.
Other changes include girls now being able to wear Mary-Jane (strap) shoes as an alternative to sandals or lace-up shoes. There are also changes to the colour of some uniform items.
"All parents were notified of the changes around December 15," Mr Southee said.
"So far, the feedback we've had has been positive."
Mr Southee said the new uniform would be introduced at the start of the 2018 school year. However, it would be gradually rolled out over the next 18 months.
"Our new Year 9 students will be wearing the new uniform, but the older students will adopt the changes over time," he said.
Mr Southee said the uniform survey had attracted about 400 responses from parents and caregivers, and around the same number from students.
"We had a mix of views, from keeping the status quo through to a complete change."
Karla, who is overseas on holiday, was happy to have been the catalyst behind the changes. She did not want to comment further as it was early in the morning when the Chronicle made contact.