The ACT and Victoria allow a student to start school if their fifth birthday falls on or before April 30 while in the Northern Territory and Queensland the cut-off is June 30.

“I would say NSW is a bit of an outlier compared to other states,” Chiang said.

“The issue of children being sent too early when they’re not ready causes problems for the child in terms of how they adjust at school.”

The trend of holding children back is particularly pronounced in Sydney, with boys more likely to start school older than girls. But researchers say it has no long-term academic benefits.

University of New England research shows students who were held back received slightly higher results in NAPLAN results on average in year 3 but that advantage dissipates by the time students reach year 9.

Co-author of that research Dr Sally Larsen said the cut-off date should be brought forward to April to reduce the gap.

“In terms of development, a year is quite a long time. If you have kids who should be in year one, there is a possibility that they will get bored and misbehave; I don’t think parents consider that aspect of it,” she