A new government target for writing and maths in primary and intermediate schools will come at a cost to other subjects, warn education unions.
It has set a goal of 80 percent of Year 8s reaching the national standards in the two subjects by the end of 2021, up from about 70 percent now.
The target was announced as one of several new Better Public Service targets and would require a much faster rate of improvement in national standards achievement.
Education Minister Nikki Kaye said the government chose maths and writing because they were important skills and national standards data showed children's achievement in the subjects dropped between Years 4 and 8.
She said a lot of schools were already setting similar goals as part of the Communities of Learning programme which grouped schools together to work on common problems.
"These are pretty consistent with a large number of Communities of Learning who are either setting this target or above this target for Year 8," she said.
Ms Kaye said the government's NCEA and early childhood participation targets had prompted huge improvements and she was confident the new national standards targets would have the same effect.
"We've seen the progress that can be made when we have these aspirational targets because naturally parents and teachers want to deliver on these."
Principals' Federation president Whetu Cormick said it was a considerable goal.
"If you look back over the last three years from 2013, 14 and 15, there have only be minute gains roughly around one percent improvement each year. So there's going to be a heck of a lot of work to be done to get our Year 8 students to that new target of 80 percent."
Mr Cormick said the new target could skew what teachers teach.
"At the moment we have a narrowing of our curriculum so I'm fearful that now that a target has been made official that teachers will be fixated on the data," he said.
Educational Institute president Lynda Stewart said that had already happened because of the the Education Ministry's target for 85 percent of children to be reaching the national standards for their age group this year, and the new target would make it worse.
"It does narrow the focus of schools yet again on particularly writing and maths," she said.
However, Ms Kaye said the new goals would not narrow the curriculum.
She said writing and maths were core skills that enabled children to do well in other subject areas.
"If you want a young person to be able to do well in science or social sciences, then these skills are crucial," she said.
"We see these as gateway areas to many other aspects of the curriculum."
Sharon Keen, the president of the Association of Intermediate and Middle Schools, said the target would make no difference to schools because they were already working toward the government's previous goal of 85 percent of 18-year-olds getting NCEA level 2.
"Part of it has been for us to strive to continually raise achievement for all our students so we probably appreciate the focus on Year 8 and some of the support it will bring to us."
Ms Keen said the target needed to be measured at a national level - not against individual schools.
The government's target would require a doubling of the recent rate at which national standards achievement had been improving - though official reports suggested that so-called improvement might actually be due to changes in teachers' understanding of how the standards work.
Ms Keen said only time would tell if the new target was achievable, though it was not just up to schools to get there.
"There's a lot more to achievement of national standards. We've got to look at our social situations, we've got poverty, we've got a number of issues that need to be addressed. If they're all addressed and we start working together, hey, perhaps we can do it."