Almost 70 per cent of year 9 students in NSW will need to sit an extra reading, writing or numeracy test to be eligible for their HSC, this year's NAPLAN data reveals.

This is the first year that the state government's new minimum literacy and numeracy standard will require year 9 students to achieve at least a NAPLAN band 8 in three areas - reading, writing and numeracy - or they will have to pass an online test in the following years to qualify for their HSC.

The preliminary results from NAPLAN, released on Wednesday, show NSW achieved some of its best results since the national tests began in 2008, topping the country in year 9 numeracy and was second for year 9 reading.

Analysis of the data also shows that NSW was first in spelling in years 3, 5, 7 and 9 and was also the top state for writing in year 5.

But despite the boost in year 9 results, most students will still have to sit the online test in one area to qualify for their HSC in 2020.

The analysis shows 68 per cent of year 9 students, or 61,015, received at least one band eight or above, 52 per cent (46,481) received at least two band eights or above and 32 per cent (28,403) attained band eight or above in all three, which means they have already qualified for their HSC.

"The results also show the NSW government's introduction of minimum standards have yielded outstanding results with students showing great improvements in literacy and numeracy," Ms Berejiklian said.

"The results for year 9 students are particularly outstanding as they mean more students than expected have now pre-qualified to meet the minimum standard of literacy and numeracy for the HSC."

In reading, 55 per cent of year 9 students received at least a band eight, while in numeracy that figure was 54 per cent. Writing was the worst test, with only 42 per cent reaching a band eight, according to the analysis.

The figures were a significant improvement on last year's results for year 9. In 2016, only 22 per cent of students achieved three band eights in reading, writing and numeracy.

Leading education academic John Hattie, of Melbourne University's Graduate School of Education, said the new standard had boosted NSW's year 9 results.

"I'm delighted to see the improved performance of NSW year 9 students in this year's NAPLAN results. A range of factors contribute to results like these, but the new HSC minimum standard can help focus school-wide efforts to ensure these improvements are sustained," Professor Hattie said.

"The HSC minimum standard will help focus teaching and learning from early childhood to year 12 to ensure all students have the literacy and numeracy skills for success in life."

But the new standard, introduced by the former education minister Adrian Piccoli, has been criticised by some parents and principals, who warned the new requirements would divide students, placed too much emphasis on NAPLAN, and would cause anxiety among teenagers.

Commenting on the national results, the Australian Curriculum, Assessment and Reporting Authority (ACARA), which runs NAPLAN, said there had been growth across most year levels and year 3 reading continued to show sustained improvement.

"Importantly, we see a gradual redistribution of students from lower bands of achievement to higher ones, particularly in some domains and year levels, such as year 3 reading," ACARA CEO Robert Randall said.

"In other areas, this improvement has not always been great enough to significantly impact average national results, but it is a positive trend."