NSW is "10 to 15 years" behind Canada, New Zealand and Finland in literacy and numeracy because too much emphasis has been placed on measures such as reducing class sizes rather than improving performance, Education Minister Adrian Piccoli says.

Mr Piccoli's comments come as this year's NAPLAN results are released to parents and schools, with national data showing some improvements in years 3 and 5 but a flatlining of results for high school students, including a drop in writing skills.

NSW students will receive their NAPLAN results from today. Credit:Dallas Kilponen

The state's overall results were strong, Mr Piccoli said, but NSW still lagged behind comparable countries and had a long way to catch up.

"NSW is not where it should be because not much happened for about a decade," Mr Piccoli said.