Students who completed Naplan online received noticeably better scores in some parts of the test than those who used paper and pencil, but Australia’s national curriculum authority says there is no problem comparing the results.

On Tuesday the Australian Curriculum Assessment and Reporting Authority (Acara) released the preliminary results for the 2018 Naplan test.

The results found that while there has been steady improvement in most areas over the last decade, students’ writing skills have continued to deteriorate markedly since the base year in 2011.

For example, the results showed the percentage of year 3 students who met the national minimum standards improved for all subjects other than writing, where it has declined from 95.3 in 2011 to 94.4 in 2018.

The release of the preliminary results confirm that there were noticeable differences in results between written and online tests.

For example, Acara said results for year 9 students who completed the writing test online were, on average, higher than the results of students who completed the writing test on paper.

Rob Randall, head of Acara, said the results were comparable, but that the difference “appears to be a result of the test mode”.

“The difference may be due to students at this year level having greater confidence writing online than on paper, as well as students’ ability to readily review and edit their work online in a way that is not possible with a paper test,” he said.

“This reinforces the benefit of moving to Naplan online, which will give teachers, students and parents more information about what students know and can do, and where additional support is needed.”

But while Acara insists the results are comparable, the difference explains the reluctance by some state authorities to release the Naplan scores.

The release of the 2018 preliminary Naplan results comes amid increasing criticism of the test. In 2018 about 20% of students across Australia completed the assessments online for the first time.

Ahead of the release of the preliminary scores Randall said state and territory authorities had confirmed “that the results for online and paper Naplan have assessed the same content and can be placed on the same Naplan assessment scale”.

However he also admitted that “individual student experiences for any single test may differ due to a range of factors, including the mode of delivery or a student’s performance on the day”.

In August it was revealed that the release was initially delayed because of disagreements between some of the states and the curriculum authority over how scores should be reported. Education department officials held a number of emergency meetings with Acara ahead of their release because of concerns about the comparability between online and written tests.

Earlier this month the Victorian education minister, James Merlino, called for an urgent review of the online test, saying it “simply isn’t good enough that data from the online tests is currently not comparable with data from the paper tests”.

Then on Monday two US academics Les Perelman and Walt Haney released a report commissioned by the New South Wales teachers federation which claimed the results were so flawed they “should be discarded”.

“There’s no way that you can successfully equate the results for a large number of schools, much less for a large number of students, to take into account the well-documented effects of mode of administration on the results of the test,” Haney told the ABC.

Acara has tried to play down those concerns, saying authorities were simply being cautious and assuring schools and parents that its methods for comparing scores were statistically valid.