Technical glitches in this year’s national literacy and numeracy tests have left a cloud of mistrust looming above initial results.

Preliminary results from this year’s NAPLAN tests were released on Wednesday by the Australian Curriculum, Assessment and Reporting Authority.

ACARA chief executive David de Carvalho says schools focused on improving student writing skills after last year’s results dropped to their lowest levels since the tests began.

“Students are to be congratulated for this year’s improvement, especially year three students, where the results are particularly encouraging,” he said.

However, students in years 7 and 9 performed below the 2011 baseline for writing.

Compared to the 2008 average, students performed better for year 5 numeracy, years 3 and 5 reading, years 3 and 5 spelling, and year 3 grammar.

This year was the second time some of the tests were taken online, with about half of the nation’s schools doing so.

The tests were plagued by technical issues when students were poised to begin in mid-May, with some students losing connectivity and others unable to log in at all.

Affected students were able to resit the tests but the issue has led to a disclaimer on the preliminary results that they should be “interpreted with care”.

ACARA insists pen and paper tests are comparable with the computer version.

Australian Education Union acting president Meredith Peace said teachers and principals shouldn’t trust the results as they are “so seriously compromised”.

“ACARA is more concerned with saving its own skin and preserving a damaging test regime than ensuring the valid, consistent and reliable assessment of student achievement,” she said.

“There is no transparency about how ACARA have arrived at the results data published today, and the community must seriously question just how rigorous the independent assessment of the NAPLAN results were.”

Deakin University education experts are also warning that the test results can’t be fully relied upon, arguing that technical glitches weakened NAPLAN’s aim of providing comparable results.

Federal Labor’s education spokeswoman Tanya Plibersek said the Morrison government has failed to reverse declines in reading, writing and maths.

“Kids need to know the basics. It’s the foundation of the rest of their education. We can’t afford for the next generation to be held back,” she told AAP.

All Australian students in years 3, 5, 7 and 9 take part in the annual tests, which cover reading, writing, spelling, grammar and punctuation, as well as numeracy.

A complete transition to online testing has been pushed back to 2021 because of this year’s issues.

A report on the underlying causes of the technical disruptions is due to soon be handed to the nation’s education ministers.

-AAP