The official cut-off date set by the Ministry of Education that determines into which year group a new entrant falls is July 1.
Essentially, this means those children born before July 1 will be classed as Year 1 in their first calendar year at school, and those after as Year 0.
Schools, however, have a degree of discretion around this date, with the majority favouring April/May as the cut-off time.
Whatever the cut-off date, there is always going to be a wide spread of ages in any class.
But for those children born on the cusp, with peers on either side, it can be a conundrum. Should they stay? Or should they go on ahead?
It was coming toward the end of the school year and I was feeling uneasy.
Our eldest daughter, Beatrice, then 6, was about to complete her second calendar year at school.
But was she ready to graduate to Year 3?
Excelling academically, we had been given the nod to attend the end of year assembly and were proud as punch. Her literacy had always been above average and we expected she would receive another certificate for her brag book.
As the names were read out, we waited for her to take to the stage. And waited.
We watched her classmates tread the boards, and still there was no mention.
Then my friends started to nudge me and whisper, and the excitement started to well in my stomach as it dawned on me that she had in fact won the trophy for her year group.
I was so proud I could pop.
Which made our decision all the harder.
Being a clever clogs is one thing but without confidence a child, or an adult for that matter, will struggle.
Our whimsical little wordsmith might have had a photographic memory for spelling but when it came to speaking up she fell to pieces. Sharing time was excruciatingly painful for her. Even having to ask the teacher a question could reduce her to tears.
I saw a broken piece of my childhood self in her and I wanted to fix it.
Born in April, Bea was one of the youngest kids in her class but, because she was coping academically, I thought nothing of it.
But as the year drew to a close and there was chatter among some of the other school mums about holding their children back, I started to reflect on the past 12 months.
She had been happy enough but hadn't expanded her social circle beyond the one girl in her class who she went to kindy with. And although the other girls in her class were all friendly and welcoming, I could see they weren't a natural fit with her age and stage.
Some of them were a whole year older than her and, while they were moving on to Hannah Montana, she was still in Disney Princess mode.
"The other kids were bigger and louder than me and I'm not very loud at school," she later told me.
I ummed and aahed and sat on the fence.
Until right at the end of the year, when I discovered she would be in a composite Year 3/4 class the following year. It was a game-changer. If she was struggling socially with those a year older than her, she would positively drown with a two-year age gap.
Going against the urge to push her forward - and it was a strong urge - I took a deep breath and asked her teacher if she could repeat Year 2.
"You won't regret it," she said.
And I didn't.
During the course of the following year, I watched as she, to coin a cliche, blossomed.
She expanded her circle of friends, read a poem out in assembly, took to the stage with a microphone in the school production and eagerly bundled something into her school bag every Friday for sharing.
Throughout the process we were open with her about why she was repeating the year and she didn't protest.
Nor did she look out of place, with half a dozen other kids in the class who, like her, had birthdays in the second quarter of the year.
The only objection she had, ironically, was that she would not be allowed to play on the school confidence course for another year, a privilege reserved for Years 3 and upwards.
Her teacher, who had made the same decision with her now teenage daughter, supported us all the way.
And although our daughter will never be the kind of kid who pushes her way to the front of the queue, I like to think that in that year we laid the foundations for her future.
The primary school teacher
Greenpark School assistant principal Christine Lees supports holding younger "cusp" children back if they are lacking in confidence.
"Always for social reasons and confidence, irrespective of academic ability and irrespective of their size too," she says.
"In primary school we don't get to see the end result but later on, when peer pressure comes into play, it's good to be confident in yourself."
Some parents resist the idea, having come through an education system that bumped smart children up a class, she adds.
"Often all parents have to go on is what happened to them at school," she says.
"We love to see children confident in themselves, irrespective of their ability, but confident in that ability."
But parents know their children best and ultimately the decision lies with them, says Lees.
"There are always children either side of the cut-off, no matter what. They might be quite okay [to go on ahead]," she says.
For those considering keeping their children with their younger peers, it is advisable to make the decision as early as possible, before they form any firm friendships, she advises.
Tahatai Coast School principal Ian Leckie, however, says unless there are special circumstances the school "tends not" to hold children back.
"That's why schools have cut-off dates," he says.
"You've always got some on the cusp but it's one of those things ... so long as it's consistently applied, you will always end up with an age range in a class, of approximately a year."
If a child has particular needs, a decision is made in consultation with parents.
"Once a decision's made it tends to be fairly immovable from that point on. You don't want to chop and change a child's classification," he says.
The secondary school teacher
Otumoetai College acting principal Ricky Feutz says it all comes down to the individual.
"You may have a young student, say a 16-year-old, in a class of 17-year-olds and, in some cases, they may be as mature or even more mature. Often they are academically competent, that's why they are in that situation, and sometimes they have the maturity to go along with that as well."
The same applies to rites of passage, such as being old enough to get a driver's licence or drink alcohol.
"Some students are keen to get their licence as soon as they possibly can, others are content to wait," says Feutz.
He doesn't believe younger students struggle any more than older students, but says older students are often more confident.
"A bit more age gives a bit more confidence to people. Having said that, you can get younger students who are very confident as well. What I have learnt about teenagers is that they [the differences between them] are many and varied."
The decision to change year groups is seldom made at secondary school level, he says.
And when a child is younger it can be difficult to judge whether they are likely to grow into their allocated year group.
"When you're talking about a 6 or 7-year-old, you are talking about a very different person from a 14, 15, 16 or 17-year-old. You don't know.
"I would struggle to say there's a hard and fast rule for this," says Feutz.
"It comes back to the individual. At the end of the day, parents hopefully know their son or daughter better than anyone else. They should talk to the school as well, consult with the school."
Tauranga child psychotherapist Augustina Driessen says if a child is stressed their education will suffer.
"I think sometimes it is a good idea to keep them back because when somebody just gets by, or gets behind, it is very, very hard to be motivated and keep concentrating. School becomes a burden rather than an enjoyment," she says.
Stresses at home can compound the problem.
"I think nowadays there are so many problems with families that I think a lot of children haven't got the confidence. It takes all their energy to hold themselves together that there's not much left for learning. If those children have the chance to have that extra year, it doesn't matter at what stage," she says.
Driessen herself was held back at secondary school and believes it was very beneficial.
"When I first went to college they suggested I stay a year behind and it was the best," she says.
University of Auckland Associate Professor Christine Rubie-Davies, head of the school of learning, development and professional practice in the faculty of education, says it is an "urban myth" that it is advantageous to be the oldest rather than the youngest in class.
"Research evidence doesn't show that ... unless the child has special needs, and even then nowadays you tend to promote those students too," she says.
"It's a bit of a conundrum within education because there is also evidence if you retain children they don't do well. Students are usually better challenged, even if it means they might struggle for a year or so."
Teacher expectations can have a negative impact on children who have been retained, she cautions.
"You know they have been retained and you perceive they are not going to do well, so you give them low-level activities. And they know their peers have moved on and they haven't."
And in New Zealand it has traditionally been Maori and Pacific Island children who have been retained, while Pakeha children have been promoted, creating inequalities.
New Zealand is the only country that she knows of where children start school on their birthday, whereas other countries tend to have one intake a year.
"Our system enables teachers to cater for individuals much better. I think it's dangerous [retaining students]. It could lead to the reason why we went away from it."
"Have them in the spring, where you're meant to," she says lightheartedly.
Zoe McClintock: I was one of the youngest, which wasn't so good when it came to things that had age restrictions, i.e. more than half the class would have their restricted before you even had your learner's. But otherwise it was great because it felt like you had more time to study, etc., after school, i.e. I graduated at 20 while my fellow classmates graduated at 21.
Helen Knight: Just recently in my diploma of environmental management, I was the oldest woman and I felt it too, especially with the younger ones there, as it was due to crappy hips and arthritis in the knees I had to pull out as there was a lot of hiking and camps that I had to go on. Not good but I lasted a year and and a bit, which was pretty good, but still felt old.
Amber O'Connell: I was youngest and in retrospect I should have been kept back with my age group rather then people a year older than me, especially in college. When I finished school and was only 17, I found it extremely hard to get a job based on my age.
Rachel Blennerhassett: I was youngest and struggled socially. Was put up at primary due to academic ability. Nowadays they don't seem to push kids up for academic ability, which I think is better. The age difference is okay in primary but is definitely more noticeable at college.
Janine Durham: I was the youngest. Hated it.
Jenene Guthrie: Youngest - always felt the others that started June the year before had a head start, while I was born in February and went straight to Year 1, no new entrant.
Donna Coburn Brown: I was one of the youngest and struggled once I hit college as I didn't have the emotional maturity for some of the situations that came up. My daughter was put forward to be jumped a year and because of my experience I refused to let it happen, keeping her with her peer group. It has worked out for the best, even though it puts her in the older age range for her year at college.
Ratana Raymond Taurua: I was the oldest, but the biggest and the tallest in my class back then. But now I'm not that big, from those days till now.
Chris Blackmore: One of the oldest but still got stick because of my size.