She moved to another school so she could do Cambridge International Exams, but it was so small - fewer than 50 students - there weren't enough teachers to keep up with her. So she turned to the books and taught herself. "It [the school] only had three teachers, it wasn't quite enough, so I had to do a lot of study by myself."
For her final year she moved to Strathallan College at Karaka, but again needed more to fuel her mind than most of the teachers could offer.
"I'm quite curious so I want to find out more about the subject and the content I'm learning, so I get a lot of things from the library and read through them by myself."
After mastering physics, English, biology and chemistry under the Cambridge examinations - she topped the world in chemistry last year - Rennie turned her thoughts to university and her school career adviser suggested applying for scholarships. She tried for three and got them all.
The first is from Auckland University, where she is studying bio-medical science, and covers her course fees and $2500 a year living allowance. The Second, worth about $30,000 over three years, is from the NZ Qualifications Authority. The third is from NZEST.