But in Cheng-Yueh Liu's case, an exception has been made.
The 17-year-old former John McGlashan pupil will skip his entire year at school this year, in favour of studying robotic engineering at the University of Canterbury.
Cheng-Yueh has been collecting NCEA credits since he was at intermediate level at John McGlashan College.
In 2008, when pupils his age were starting NCEA level 1, Cheng-Yueh passed NCEA level 3 and gained University Entrance.
Last year, he did NCEA level 3 again and received an excellence endorsement, he received five scholarships in NCEA level 4, was co-dux of the school and, to top his year off, he retained an A+ average in mathematics papers at Canterbury University - all before he had started his final year at secondary school.
Not bad for a Taiwanese boy who came to New Zealand aged 5 not being able to speak a word of English.
Not surprisingly, Cheng-Yueh has decided to skip year 13 and head straight to Canterbury University, where he will study engineering, specialising in megatronics (robotics).
It is fair to say, Cheng-Yueh is every teacher's dream pupil.
But by the same token, he is also considered a nightmare.
A pupil in the classroom who probably knows as much, if not more than the teacher, can be challenging to keep stimulated.
Principal Mike Corkery said Cheng-Yueh's results were "all the more remarkable", considering he gained two scholarships while still in year 11.
"That gives him a bag of seven scholarships before reaching year 13, and that has to be some sort of national record."
Mr Corkery acknowledged Cheng-Yueh's capacity for hard work, his academic giftedness, his humility and his good nature.
Cheng-Yueh said if he had not been so young, and not lacked a couple of extra NCEA credits, he would have gone to university last year.
He attributed much of his success to his parents and John McGlashan College.
"Ever since our TV broke, my Dad didn't want to buy a new one because he wanted me to focus on my studies," he said.
Cheng-Yueh spends much of his spare time studying - up to five hours a day - but insists it is not a chore.
"I just enjoy studying. Sometimes during the weekends, I get so bored. So I read books and do mathematics - it's my favourite subject.
"I haven't got bored at school because they've always provided challenging and stimulating subjects at a higher level for me.
"Having said that, I'm a mature person and I need to go get on with life now," he said.
