The Canberra Liberals have suggested an extension of school hours to "meet the modern demands of a working family", an idea the teachers' union has snubbed as an ill-conceived thought bubble.

In an interview with ABC Radio Canberra, the Liberals' education spokesman Andrew Wall questioned whether a 9:00am-3:00pm school day was still appropriate in 2018, and proposed mirroring overseas models of 8:00am-4:00pm class schedules.

The comments were made in a debate about the ACT Government's tightening of cross-border enrolments, which will see NSW families restricted to sending their children to a small number of ACT schools.

In a pre-empted comment, Mr Wall said the Canberra Liberals were developing a discussion paper on "producing competitive young people for a global job market" as the Australia and the ACT continues to slip further behind international education rankings.

That discussion paper would include looking into whether the school day was long enough, he said.

"Are we getting everything into the school day that we need to?" Mr Wall said.

New kindergarten students at Fraser Primary School in Canberra. ( ABC News: Elise Pianegonda )

"Perhaps an idea might be mirroring what's done overseas, which is a much more academic focus in the morning, and of an afternoon is the extra-curricular and community-based activities, to develop a well-rounded individual.

"That could include increasing the length of the school day."

"So [it would] take some of the burden off parents and also give a clear opportunity of delivering well-rounded education."

'Destined to fail'

The ACT Education Minister Yvette Berry criticised Mr Wall's comments and indicated no plans to consider the proposal.

"That's certainly not something that I've been hearing from parents and students in the conversations I've been having over the last 12 months," Ms Berry said.

"And I think it would be a very dangerous thing to come out with a thought bubble like that, for our community as a whole."

Australian Education Union ACT secretary Glenn Fowler said he was disappointed teachers had not been consulted with for the discussion paper.

"I urge the Canberra Liberals to open communication channels rather than blindsiding people in the media," he said.

"We represent 3,500 Canberra professionals that would be affected by this and we've never heard about it."

"If the Canberra Liberals prepare a discussion paper about education without talking to teachers, it is destined to fail."

Mr Fowler said he would look at the proposal once it becomes more than a thought bubble, but he held immediate concern about immediate teacher workload.

But Mr Wall later said the conversation was in its very early stage and was occurring in "close circles," with wider consultation to follow the release of the discussion paper in coming months.

He said there would be opportunities to explore flexible teaching options to address workloads.

Flexibility improves productivity, motivation: principal

A Melbourne school that has adapted longer and more flexible school hours says the model works. ( File photo: ABC News )

Schools in the United Kingdom and the United States have increased hours, with many focusing on more extra-curricular activities such as sport and art.

But some Australian schools have also adapted a flexible approach.

North Melbourne high school, Templestowe College, staggers classes from 7:15am-5:15pm throughout the week. They give students the choice for early starts or early finishes, with options to alternate between longer and shorter days.

Principal Peter Ellis said the flexibility had generally improved student productivity and motivation.

"We know people are either morning or afternoon people so it was about giving them choice," Mr Ellis said.

"Typically within our timetable we do aim to have more academic subjects early in the day and a more practical hands-on [approach] in the afternoon.

"Giving them that change of structure and the choice has made them get more work done, especially in the afternoons."

Federal Education Minister Simon Birmingham has previously stated that he would be open to the idea of funding schools to have extended open hours, saying it would help improve student performance.

But ultimately, he said the decision lies with state and territory governments.