In a recent budget submission, the ACT Council of Parents and Citizens Associations warned schools were bracing for "significant population growth" over the next decade and called on the government to build a multi-storey school in the inner north as well as a campus in east Gungahlin and a new primary school in central Belconnen.

Almost 20 per cent of Canberra public schools are full or almost full, according to 2018 government census data.

Janelle Kennard of the council said the government's own projections indicated Gungahlin school populations will double over the next decade - with an addition of almost 7000 students - but planning remained too conservative.

Some demand will be met by a school opening next year in Taylor and construction of another school in Molonglo will also begin in 2019 as land is released for future school sites.

But Ms Kennard said a number of preschoolers were already missing out on spots at their local schools, separating them from their friendship groups and causing hassles for families with several kids at different schools.

Development along the light rail corridor of the inner north had put "strain" on schools such as Lyneham High, Campbell High and North Ainslie Primary which were filling up or already over capacity, the council said.

It recommended buying a smaller parcel of land for a vertical school, in line with models rolled out in Sydney and Melbourne.

“Let’s not limit ourselves by what we’ve done in the past. Canberra’s growing up," Ms Kennard said.

ACT Education Minister Yvette Berry said the government had invested more than $24 million in school expansions to meet enrolment needs in the last budget but would consider the group's submission.

"I have visited the vertical school in Melbourne and although Canberra is a bit different it’s always good to see creative solutions such as this," she said.

While in Canberra overcrowding wasn't forcing students to work in corridors or courtyards, Ms Kennard said demountables rolled out across ACT schools were not enough to cope with the pace of growth.

"Then you’re not going to have enough things like toilets, parking or a big enough hall, you’re going beyond what the school was designed for," she said.

Parents reported specialist facilities such as art rooms, libraries or halls were often the first to go when a school faced capacity issues, the council said.

"In Canberra, libraries are being replaced as permanent classrooms," Ms Kennard said.

Some specialist classrooms are still counted in capacity figures and the council wants them excluded from such calculations.

"It wasn't long ago that we had a policy to close schools, we don't want to repeat that pattern," Ms Kennard said.

"But we think they're being too conservative and leading too far [the other] way. There’s been too much of a squeeze while a baby boom is happening. What we’re now seeing in Belconnen and in central Canberra ... we could do with some of those schools back."

A review of census data earlier this year ruled out some areas like kitchens and art rooms from counts, the directorate said, slightly lowering capacity figures, but specialist classrooms could still be included in data as schools were measured on a "case by case" basis.

While 15 Canberra schools were close to bursting at between 102 and 90 per cent capacity as of February, a dozen others were less than half full.

After a number of Canberra schools grappled with capacity issues in 2017, the ACT changed the rules on cross-border enrolment to limit the number of schools NSW families could send their children.

The education directorate says there are guidelines for new school builds which dictate the number of students per square metre in a classroom, but there are no set rules for existing buildings.

It is understood principals are guided by student-teacher ratios, which are still among the lowest in the country.