The final results of the 2019 NAPLAN tests, released on Tuesday, show writing improved across all years in all states and territories compared with the previous year.

But for Years 5, 7 and 9, those results are still lower than the base year of 2011, the first time comparable tests were done.

The head of national testing authority ACARA, David de Carvalho, described the results as a national upward movement.

"I don't think we can get too excited about this at this stage, one swallow does not make a summer, but if this was to be repeated, this kind of improvement in the coming NAPLAN results, it would be an encouraging trend," he said.

"What happens in 2020 will be an important source of information about what might be behind the change."

The results showed the beneficial way NAPLAN could call attention to problems.

"We've had a national debate about our declining writing results in NAPLAN over the last few years," Mr de Carvalho said.

"One possible explanation for the uptick last year was that the renewed efforts and focus on writing that has been undertaken across jurisdictions is bearing fruit."

Some states have questioned the usefulness of NAPLAN, with NSW, Queensland and Victoria reviewing whether the standardised testing gives parents and teachers diagnostic information in the most efficient way.

Federal Education Minister Dan Tehan said the tests did provide valuable information.

"The Morrison government continues to back NAPLAN because our community deserves to know how our students and schools are performing," he said.

Critics have also suggested the tests are behind an apparent flatlining of student results over time.

Before NAPLAN was instituted in 2008, there was no nationally consistent testing to compare the achievements of all students.

Mr de Carvalho said it wasn't correct to say results were flatlining, highlighting improvements in the average scores in most domains and years in the decade since testing began.

Those improvements are most pronounced in the primary school years, a trend Mr de Carvalho said was also seen in international results.

Labor's education spokeswoman Tanya Plibersek said the latest results combined with those from international testing did not paint a pretty picture of Australian students and the nation couldn't afford for the next generation to be held back.

Australian Associated Press