The $2.45 million expansion comes after a long-running push from parents in Canberra's fastest-growing region, where schools have begun to struggle with capacity.

On Thursday, ACT Education Minister Yvette Berry announced Year 3 classes will begin from next year at the Franklin school. That means means students in Year 2 will be assured a place next year, becoming the first class to continue through to Year Six as part of the staged expansion.

The development was a 2016 election promise but parents groups had previously criticised the delay in getting money set aside in the ACT budget.

The Franklin school is already at capacity, Principal Julie Cooper said, with 312 students from pre-school up.

"The birth rates within the Gungahlin area have changed [since the school opened in 2013]...and also there are so many more new suburbs around so of course, with the shifting sands of community, this is a response from my community to the politicians," she said.

Ms Berry said the new expansion into Year 6 would retain the 'feel and culture" of the early childhood model that worked for the Frankin school's students.

The Barr government had invested more than $270 million in Gungahlin school infrastructure over the past decade, she said, brushing off assertions schools in Canberra's north were "bursting at the seams".

A spokeswoman for the Franklin Early Childhood School Parents and Citizens Association welcomed the news on Thursday.

"My son is really excited he'll get to stay on and see all his friends all the way through primary school," she said.

"We know a lot of families haven't been able to get into the school in the last [two] years so it's really exciting."

Local member Meegan Fitzharris said she had been speaking with families for "some time" about the need to grow the school.

A survey conducted by the parents' association late last year found more than 96 per cent of families supported the expansion.