Primary school pass rates have virtually flatlined despite an six-year government literacy and numeracy "crusade" costing more than $250 million.

Data shows a quarter of children entering high school are below the National Standards in reading, writing and maths.

LISTEN ABOVE: NZEI PRESIDENT LOUISE GREEN EDUCATION MINISTER HEKIA PARATA INTERVIEWED BY MIKE HOSKING 

Of the almost 60,000 students who began Year 9 last year, 17,900 were unable to meet writing requirements, 18,500 were behind in maths, and 12,700 could not read at the expected level, meaning they would have to be rapidly "caught up" to have any hope of passing a high school qualification.

The figures remained largely unchanged over three years, rising an average 1 per cent across all year levels since 2012.

Chief Education Scientific Adviser Professor Stuart McNaughton said experts knew many of the reasons why children were falling behind and were already acting on those, but urged that more could be done to lift achievement.

"The number we have set isn't 'magic'. In principle we should be able to get a higher proportion of students up to the standard."

Professor McNaughton said a 1 per cent gain meant up to 4000 more students reaching the standard each year. A small, incremental increase across a large system was still a positive, he said.

The Herald will also examine patterns in the National Standards results, which was able to be evaluated as a trend for the first time with the publication of three years of in-depth data. Analysis shows significant variability across subjects, and by gender, ethnicity and socio-economic status.

Educators say the minimal level of improvement raised questions about whether the hugely controversial National Standards initiative has worked as intended.

"It bears out what the profession said at the time - that the standards wouldn't be enough. They give us a broad look at where a child sits within an age group but don't tell us what their strengths and weaknesses are or what to do next," said long-time primary school principal Frances Nelson.

"It hasn't become critical to teaching and learning. It hasn't been the silver bullet. So why spend all that money on something we didn't need?"