Last year's 100 per cent across all levels was also an improvement on 2014s results - the school achieved 100 per cent pass rates in levels 1 and 2, and 95.5 per cent in Level 3.
The increase was said to be a result of dedication, drive, and commitment from the girls, the staff, boards and parents.
The school did not drive "the girls just for percentages", but girls drove themselves to learn and achieve, Mrs Peterson said.
Teachers also went the extra mile to help students achieve their goals, through extended lessons, and tutorials during lunch time or holidays.
"We're here to support them, we're here to provide the structure and the scaffold and the opportunities," Mrs Peterson said.
"Our girls want to go into successful tertiary employment pathways, they want to be leaders in their field.
"It's not unusual for them to have highly aspirational goals in their own individual pathway," she said.
The school establishes high expectations for students when they begin in Year 7, so girls can face the "academic rigour" of the senior school, Mrs Peterson said.
"They enjoy success. They get a taste of that in the intermediate years, that feeling of feeling good about yourself, that you are always striving to achieve your personal best whether that be in the classroom, or on the sports field, or in the cultural arena."
While other qualifications had their benefits, Mrs Peterson said they found NCEA was a good vehicle for girls to meet their credentials for their education pathway.
"We call it learner-centred here rather than learning-centred, so it's the girl at the heart of it.
"The wonderful thing about NCEA is it allows us the capacity to customise or personalise a learning programme for an individual student."
The school also uses "incentivised learning" to reward success.
When the 2015 NCEA results came out, students were rewarded with free icecreams from the Edge radio station, and staff celebrated at St George's, she said.
