Education Minister Hekia Parata says she is unconcerned by a report showing a high error rate in teachers' use of the national standards.
A report for the Ministry of Education says 49% of teachers' judgements of children's writing last year were wrong, as were 39% of their maths assessments.
Ms Parata says the Government has a five-year plan to improve teachers' use of the standards.
She told a Post Primary Teachers Association conference in Wellington on Wednesday that there is variability, but it will get better.
The report, conducted by Maths Technology for the ministry, says when teachers were wrong in their judgement of children's work, they tended to rate it better than it was.
It says the results call into question the dependability of the overall teacher judgement that decides if a child has reached the standards.
The Ministry of Education said the error rate in schools' final results would not be as high, because these are based on several examples of each child's work.
The ministry said a more accurate measure of teachers' judgement, using four pieces of assessment evidence, showed more than 81% accuracy for writing and up to 90% for mathematics.
However, in that exercise, the four pieces of evidence had already been correctly ranked against the standards and teachers did not have to work it out for themselves.
Principals Federation president Paul Drummond says though the average accuracy rate for writing across 546 samples of of work was about 51%, there were big swings in accuracy on individual samples. He says it means schools' results should never have been published.
The primary teachers' union says it is misleading and dangerous to put out wrong information and the national standards website should be shut down. President Ian Leckie says correct data is not possible when teachers have to interpret what they think the standards mean and fixing the problems is a waste of time and money.
The head of Massey University's School of Educational Studies, Howard Lee, says school results recently published online are probably just as inaccurate.
"We have to be very, very careful in using this data as a ready reckoner of educational achievement in schools ... it isn't robust in any shape or form."
Teachers 'not at fault'
Principals say teachers can't be blamed for having a high error rate in marking.
Mt Cook School principal Sandra McCallum says it is incredibly unrealistic to get consistency across the standards in such a short time.
She said there had been no guidelines from the Ministry of Education on what is at or above the standard so people are making their own judgements
Stratford Primary School principal Kelvin Squire says the problem is that the data should only be a signpost for how a student is doing. He says teachers are not failing with their assessments.
Teachers dismissive of Parata's speech
At the Post Primary Teachers Association conference, Hekia Parata also emphasised the need for teachers to improve education for under-achieving students, but her comments left the union's members feeling upset and disappointed.
The speech focused on the need to lift an already good education system by doing better for Maori and Pasifika children, but teachers say the speech was insulting and showed the minister does not know how modern secondary schools operate.
They say Ms Parata's comments about correct pronunciation of children's names and about the content of the history curriculum show she does not know how much schools have changed.
Radio New Zealand's education correspondent at the conference says the speech was greeted with derisive laughter, while some teachers chatted among themselves. He says teachers feel she has no plans to improve education beyond hectoring teachers.