St Gerard's School pupil Dani Dowling said she did not like the fact girls could only wear the school kilt and did not have the option to wear dress pants during winter.
The year 7 pupil took it upon herself to make a presentation to the school's board of trustees as she disliked the idea girls did not have the same choice as boys for winter uniform attire.
Principal Trina Eastwood said about a dozen girls had opted for trousers and were waiting for orders to arrive.
Earlier this year the board invited Dani to make a presentation to the board.
She pleaded her case for about 20 minutes at last month's board meeting, wearing the preferred trousers.
Her mum, Lara Dowling, said she was ''blown away'' by the amount of work she did.
Dani said it was about giving the girls a choice and not taking the kilt away.
''I made the speech in a way that they couldn't say no.''
In completing the groundwork, Dani spoke to pupils, parents and other community members and identified the trousers she wanted, over a six-week period.
She also researched ''gender equality'' and referred to the likes of Kate Sheppard, Helen Clark and Prime Minister Jacinda Ardern in her presentation.
Ms Eastwood said Dani highlighted the fact female staff members at the school also wore trousers.
''She had really good examples.''
Board acting chairwoman Ellen Middendorf said after some discussion following the presentation a motion was approved to add the trouser option to the girls' winter uniform.
''It was really rewarding to see Dani had identified something which affected, not just her personally, but other students, and that she felt she could take action and come forward to share her proposal with the school's board.''
The St Gerard's School student council had surveyed pupils in 2018, about whether to make changes to the winter uniform, and over 70% of the female pupils supported some sort of change, Ms Middendorf said.
A full uniform review will be done in 2020.
