The writing skills of primary and high school students sitting NAPLAN exams have dropped to their lowest level since nationwide testing began.
The results for this year's NAPLAN tests showed students in years 5, 7 and 9 had writing test results that were "well below" those recorded in 2011, the first year that writing testing began.
However the controversial testing regime showed improvements in some other areas, preliminary NAPLAN data released on Tuesday showed.
Numeracy results for students in years 5 and 9 were "significantly above" the average in 2008 when those skills began being subject to national testing.
Reading and spelling results for years 3 and 5, and grammar results for years 3 and 7 were also "significantly above" the NAPLAN 2008 average.
Compared with last year though, results across the board were stable.
The tests faced a new barrage of criticism this year because about one-in-five students were able to complete their exams online for the first time.
Some teachers argued that the results of students who sat tests online should not be compared to those completed by those who used pen and paper.
The Australian Curriculum, Assessment and Reporting Authority, which organises the NAPLAN tests, says online and paper results are comparable, but noted that the method of testing can affect results.
Meanwhile, a scathing review of the 2018 NAPLAN tests by American education experts Les Perelman, formerly of MIT, and Professor Walter Haney, of Boston College, recommended that this year's results "should be discarded".
The experts said this year's NAPLAN tests were so flawed that its results were of limited use to students, teachers, parents and schools.
Their review was released by the NSW Teachers Federation, whose president Maurie Mulheron said it wasn't fair that this year's test had manipulated the results of students doing online exams and those using pen and paper.
"The attempt to equate the two different modes of testing is unfair and invalid," Mr Mulheron said.
But outgoing federal education minister Simon Birmingham has praised the use of online testing, saying the eventual uptake of the online system will provide faster turnaround of results and more detailed feedback for students.
"The best way for each teacher, parent or school to get the most out of NAPLAN in the future will be for all schools to move to the online format," he said.
Final national results for the standardised tests are set to be released towards the end of the year.
INITIAL NAPLAN RESULTS:
* No significant changes compared with last year
* Areas significantly above the 2008 average:
- Years five and nine: Numeracy
- Years three and five: Reading
- Years three and five: Spelling
- Years three and seven: Grammar
* Areas well below 2011 results:
- Years five, seven and nine: Writing.
Australian Associated Press