Ms Berry made the claim defending her government's record on school achievement during Question Time in the ACT Legislative Assembly after the Institute's report was released on Tuesday.

But report co-author Peter Goss said while he believed the territory's education directorate was going in the right direction, it was not about intentions, rather whether implementation and results in schools was making a difference.

The report showed the ACT was the worst performer of all states and territories and on a like for like basis, Canberra students made two to three months' less progress in two years of NAPLAN data assessed than the national average for both primary and high school students.

Asked by Opposition MLA Mark Parton why she was blaming the government's poor performance on NAPLAN, Ms Berry said she had made no such claim, rather she was concerned about how the data was used and compared from school to school.

Ms Berry also said the data used was two years old, provided a very narrow view of the territory's schools and the government was already working to implement all the report's recommendation as part of an overhaul of the school system.

But Mr Goss, the institute's education program director, said the analysis in the report was always retrospective, and what was strong and rigorous about the research was being able to see the trend over half a decade.

He said the institute began its research a year-and-a-half ago, on data including 2016, and if it had delayed it could have possibly obtained 2017 data, but the 2018 data had not been released.

"I can't really see what's in her mind, this is not a comment on any particular minister, this is a genuine attempt to identify what is working well and what is not working well, because if we identify when things are working, we can do more of them," he said.

Mr Goss said while there were weaknesses in NAPLAN data, it was the most comprehensive data on student performance available, and the approach the institute took of looking at progress over time and comparing like for like, was the most robust way to assess what progress was being made.

He said despite concerns about the effects of NAPLAN testing, reading, writing and numeracy achievement did matter, as such skills were the foundations of learning and children needed to build strong foundations to go on to learn more complex material.

"My understanding is the ACT government has been aware of this relative underperformance for some time, and it has been acting on it," he said.

"The discussions I've had seem to be that the government's intentions are directionally correct, but I haven't gone into great detail on that, but I'm delighted to hear the minister feels the territory is acting on all the recommendations.

"But what will matter in the end is how well-implemented those policies are, in the end, it's not about intentions, it's what actually happens in each classroom and each school that has the biggest impact on student outcomes."