This year, half of Australian schools are holding the national literacy and numeracy test online, ahead of a complete transition to more precise computer-based testing next year.

Connectivity issues with the online platform this week have forced crisis talks around the country as some states weigh up a return to the old paper test.

Of the 150 schools in Canberra, just three are sticking to paper this year, following a similarly strong uptake of 93 per cent of schools sitting the test online in 2018.

About lunchtime on Tuesday, the Catholic Education Office's internet network for Canberra schools crashed due to an unrelated but unfortunately timed broken fibre optic cable.

The network was down until about 4pm when technicians were able to restore it, office director Ross Fox confirmed.

But Canberra students were also among those affected by glitches in the national testing platform on Tuesday while sitting the writing test.

An ACT government spokesman said only a small number faced a white screen, and less than one per cent of students had their tests suspended.

"Arrangements are being made to ensure that these students are not disadvantaged," he said.

The spokesman said the non-government school network outage would not disadvantage those students either as test protocols already existed to manage such contingencies.

"Thursday has been incident free and thousands of students are busy undertaking their NAPLAN tests online all across the ACT," he said.

National assessment authority ACARA said 750,000 online tests were completed successfully on Tuesday and Wednesday but it was continuing to investigate the causes of "connectivity issues" experienced by some schools.

A spokesman said any inconvenience caused to students was regrettable and said procedures were in place if issues continued, including sitting paper tests as a last resort.

"The technology and logistics of a national online project of this size are highly complex," he said.

Mr Fox said, while the disruption had been significant, he was confident the network issues had been resolved.

"In life, not everything goes according to plan," he said.

"This is not ideal, but we still see [NAPLAN] as really valuable. I expect schools will use this as a learning opportunity."

Amid debate on the usefulness of the test, Mr Fox said it was important NAPLAN was put in its proper context as one of many assessments for teachers and parents.

"I've been concerned about the unnecessary anxiety people have created around it," he said.

"Schools are more than just test results, but life involves tests. This is not a high stakes test, it's a diagnostic assessment."

The Australian Education Union said this week's NAPLAN glitches demonstrated the test was not fit for purpose and lashed the Coalition for resisting calls for a full review of the assessment last year.