The gap between girls' and boys' achievement in the classroom is widening further.
And as the latest release of National Standards data has revealed the growing gender gap, a new book says the controversial standards are narrowing what primary school children are learning.
The new data shows a gap between girls and boys of 16 percentage points in writing, the widest gap since national standards were introduced in 2010.
• Big read: National Standards: Are they working?
The proportion of girls achieving the writing standards was unchanged at 79.4 per cent, but boys reaching the standards fell slightly from 63.9 per cent in 2015 to 63.4 per cent in 2016.
Boys also lag behind in reading, with 73.6 per cent achieving standards compared with 82.1 per cent of girls - both down 0.3 per cent from 2015.
However, boys have almost caught up with girls in mathematics, climbing from 74.8 per cent achieving standard in 2015 to 75 per cent last year, a sliver behind girls on 75.9 per cent.
Massey University literacy expert Professor Tim Nicholson said girls outperformed boys in literacy in every developed country by an average of one year's learning, but there was still debate about the extent to which this was biological or cultural.
"Boys definitely are not as quick as girls to grow in cognitive development and fine motor skills," he said.
"But it could also be that social-stereotyping thing - 'boys will be boys, we don't really want to push them into academic things, that's sort of a girl thing, reading books and so on.'"
He said teachers needed to try different strategies with boys, such as giving them goals for how many extra words or subjects they would include in their next story.
"I'm amazed at how there are lots of strategies that would be really good for boys that we are not using," he said.
Ethnically, the latest data show a slight narrowing of the gap between European and Pasifika students from 19.7 percentage points in 2013 to 18.2 points in 2016 in reading, from 18.7 to 16.6 points in writing, and from 18.9 to 18.1 points in maths.
But the gap between European and Māori students has been unchanged at between 15.2 and 15.7 points in every subject in every year since 2013.
Meanwhile a new book by Waikato University educationalist Professor Martin Thrupp says national standards have narrowed what primary school children are learning.
He says the standards have led to better targeting of students who are falling behind, have helped many teachers to improve their teaching, and have boosted the motivation of some teachers and children.
But he concludes: "Such gains are overshadowed by damage being done through the intensification of staff workloads, curriculum narrowing and the reinforcement of a two-tier curriculum, the positioning and labelling of children, and unproductive new tensions among school staff."
An in-depth study of six schools which Thrupp led found that the pressure to concentrate on literacy and numeracy was much greater in schools serving low-income families, where many children were below the standards.
In contrast, children from better-off families were more likely to be reaching the standards, so their schools could afford to spend time on other subjects such as science, social studies, the arts and sport.
In effect, the standards were "reinforcing a two-tier curriculum" - a narrow one for poorer children and a wider one for middle-class children.
Education Minister Nikki Kaye said she made no apology for driving primary schools to focus on literacy and numeracy because they were "foundation skills required to participate in the community and to access other areas of the curriculum".
• The Search for Better Educational Standards: A Cautionary Tale, by Martin Thrupp, will be published by Springer on September 11.