Parents are increasingly delaying starting their children at school by a year, even though education experts warn holding a child back generally results in no long-term learning advantage.
As school starts back this week, up to a fifth of kindergarten students will be entering school a year later than they were eligible to attend.
NSW Department of Education figures show 19.5 per cent of kindergarten children were already six when they started kindergarten last year, compared with 17.3 per cent in 2002.
In NSW, children can start kindergarten if they turn 5 by July 31 that year. By law, all children must be enrolled in school by their sixth birthday, which means there can be an 18-month age gap between students in some classes.
While many parents believe their child will cope better with the demands of school if they are one of the older students in their class (particularly if they are boys), research shows any initial advantage dissipates as children progress through school.
''Most kids entering school on time at age have no disadvantage to them,'' University of Sydney education professor Andrew Martin said, but added that, in some instances, it might be necessary to hold some children back.
''For nine out of 10 kids on-time entry is appropriate. They might be a little bit young, there will be a bit of catch-up in the early days, but have a long view of your child's education. Before you know it they will be catching up.''
Professor Martin said older kindergarten children tended to be more physically and emotionally capable than their younger peers. ''Some children have a whole year of life on other kids in the class. At that age that's a big developmental difference,'' he said.
Charles Sturt University professor of transition to school, Bob Perry, said this was reflected in the results of the NSW Government's Best Start Kindergarten Assessment program, which tests the literacy and numeracy skills and understanding of the incoming students. But the age-related developmental differences fade as children grow up.
''By mid to upper primary, whatever edge you think they may be getting [evidence suggests] for most kids it is ironed out,'' Professor Martin said.
Professor Perry concurred. ''After three or four years it pretty much evens out,'' he said.
''It's not always the older kids doing better. Some younger kids learn faster.''
Research has shown that by high school younger children are often more motivated and engaged in their studies than their older peers.
''The younger kids are not ahead of themselves in their mind, they don't have a licence and want to be off driving four months out from the HSC,'' Professor Martin said.
Education experts advised that, while parents may be concerned their child can't hold their pencil properly or don't know the alphabet when it comes time to start school, that is actually what school is for.
''It's not whether they can read or not, the teacher thinks that's their job to do,'' Professor Perry said, while noting that some schools appear to discourage the enrolment of younger children by organising their wait lists by birth date.
Professor Perry favours the New Zealand approach where children start school the week they turn five, regardless of when that occurs in the academic year.
He said a child's school readiness was best gauged by their desire to go to school, their ability to interact with other children, and whether they can keep control of their belongings.
''Having a successful start to school is not about what you know, it's about how you know it, and if you've got friends going you'll have a happier time than if you didn't,'' Professor Perry said.