NSW Premier Dominic Perrottet mentioned the idea of changing the formal hours of schools across the state earlier this week as a possible measure for helping parents with the day-to-day shuffle of life.

The idea has been slammed by NSW Teachers Federation president Angelo Gavrielatos as a "distraction" of the real issues surrounding education.

He said if the Premier was worried about the pressures of working families he should announce funding for before and after school care as well as funding for a preschool for every primary school.

"We have a serious teacher shortage driven by uncompetitive salaries and unsustainable workloads and rather than tackling that issue we have the government announcing another slogan with respect to the operating hours of schools."

However, Dapto High School principal Andrew FitzSimons said exploring a trial seemed a sensible idea.

He said the school's start time of 8.28am was one of the earliest for a public high school in the Illawarra region of NSW.

"I think the research says that adolescents, particularly males like to stay up late and get up late," Mr FitzSimons said.

"If you were running a school for the benefits of adolescents you would probably start at 10am. But schools are just part of an incredibly complex set of community arrangements."

School buses and long commutes dictate the schooling hours at Calrossy Anglican School more than principal David Smith would like.

The NSW north-east school, based in Tamworth, starts lessons at 8:40am, later than Mr Smith thinks ideal.

However, the school buses travel from nearby towns Gunnedah and Quirindi and those doing out of town runs struggle to get the kids to the gates on time.

Mr Smith said it meant a lot of Calrossy students had to get up early and got home late.

"I'm a little bit concerned that because of the buses and the distance people have to travel, we end up having a shorter day, and I don't want country kids to miss out," Mr Smith said.

He would like to see a longer school day for Calrossy students - at the moment students are cutting time out of their lunch breaks to get additional lesson time. A longer day could mean more break time.

Edmund Rice College, a Catholic all-boys secondary school in Mount Keira in NSW's Ilawarra, switched to an 8am to 2pm day for all students after extensive consultation.

"It's always been a positive element to our school and it's a point of difference that works for us," principal Stephen Gough said.

Mr Gough said it allowed students more time to pursue extra-curricular activities including part-time work, representative sport and after-school study groups.

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NSW Teachers Federation president Angelo Gavrielatos said school hours already varied from school to school across the state - based on a range of factors, both local and historical.

"What works in one school may be considered an anathema in another school.

"The variation of school hours where it does occur requires significant consultation and a consensus across literally hundreds and hundreds, if not thousands, of people."

Mr Gavrielatos said it was important to remember that schools were for teaching and learning "and the supervision of kids is a bi-product of schooling during those hours".

More flexible school arrangements can be found in a number of countries overseas.

Brazil, China, South Africa and South Korea have school start times ranging from 7am to 8am.

In France, students are in school for eight hours from 8am some days, but most get Wednesday afternoon off.

Long lunch breaks allowing students to go home to eat with family are built in to many school schedules in Japan and Spain.

Students in South Korea are provided with lunch, with school running from 7:30am until 2pm.