The number of demountable classroom buildings used in ACT public schools has fallen over the past decade, despite an increase in the territory's student population.
Figures from the ACT education directorate showed as of July 2017, there were 73 demountable buildings across Canberra public schools, making up 130 classrooms.
A demountable building can include between one and three classrooms.
During the past 10 years the number of demountables has fallen from 87 buildings used in 2008, which at the time made up 144 classrooms.
Janelle Kennard from the ACT Council of Parents and Citizens Association said she was surprised the number of demountables across ACT public schools had fallen despite the increase to student numbers.
"At our monthly meetings, we're hearing more and more problems and concerns from parents around capacity issues with public schools, and it's surprising that there's fewer demountables," she said.
"I'm a bit baffled by that."
Ms Kennard said some school halls no longer had room for parents to attend school assemblies, with facilities reaching capacity due to a boost in student enrolments.
While she said demountables were a good solution to meet the need of a growing student population more forward thinking on the issue was needed.
"We have to be careful when it comes to long-term planning, with adequate school planning in Canberra, and a willingness to build more schools is required," she said.
A spokeswoman for the directorate said the decrease was due to multiple factors.
"Over the last 10-year period, some new transportable buildings have been procured, some have been relocated and some that have reached the end of their life have been disposed of," the spokeswoman said.
School enrolments continue to climb in the ACT, with some forced to use libraries or community rooms as classroom spaces.
The most recent ACT school census showed there was a 3.8 per cent jump in the number of enrolments at public schools this year, rising more than 1700 students from last year.
In the past four years, student numbers at all ACT schools have increased by 9.6 per cent, or 6583 students.
The directorate spokeswoman said the average serviceable life of a demountable classroom was between 15 and 20 years, and it was one of the strategies used to deal with a rise in student enrolments.
"The directorate's approach is to use transportable [classrooms] when there is a short-to-medium term peak in student numbers at a school, and when student enrolments differ to the modelled projections," she said.
"Transportables can also be moved within the school system, allowing for flexibility in use of infrastructure and reducing the risk of creating facilities that are not needed in the long term."
Three demountable buildings were installed during the past financial year, with two of them at Neville Bonner Primary School and one for Palmerston Primary School.
It's expected four demountables will be installed over the coming year.
Figures from the directorate show Amaroo School and Gold Creek School have the most demountables, with seven buildings each.
Australian Education Union ACT branch secretary Glenn Fowler said while the union holds no position on the issue of demountable classrooms, class size was an important topic.
"Demountables come and go and we don't have a blanket position on them. We're happy to listen to experts on demographics and we're not inflexible about it," he said.
"Every child must be guaranteed an education at their local public school and they deserve to be educated in a fit-for-purpose, 21st century learning environment."