Most schools are using national standards effectively but 20 per cent are either philosophically opposed or struggling to implement them, the Education Review Office says.
National standards have faced criticism from some teachers and school boards since their introduction in 2010, with some schools refusing to implement them.
ERO chief executive Graham Stoop told a parliamentary select committee today that a report last year found 10 per cent of schools were opposed to national standards.
"At least 80 per cent of schools are getting on with business of implementing national standards. Ten per cent of schools are struggling, because there might be capacity issues perhaps. There's another small group, around about 10 per cent from our last report, that are opposed."
Dr Stoop said in the past, schools were not collecting student achievement data and there had been "significant gaps" in schools' assessment practices, but with national standards in place schools were able to provide the ERO with that data.
ERO national evaluation services manager Diana Anderson said there was a small group of schools philosophically opposed to the standards, but the number had fallen since the last report.
An increasing number of schools were now using standards more and more effectively, she said.
"It's gradually becoming more and more business-as-usual for more and more schools. Schools are obviously on a continuum, and we have a small group of schools still who are not doing well with the national standards.
"But that group size has got smaller - particularly the ones that are in direct opposition is a very small number now."
Ms Anderson said in the schools that were struggling to implement the standards, there were often governance issues that distracted from the primary business of student achievement.
Labour education spokeswoman Nanaia Mahuta said she was not aware of a school that fully endorsed national standards.
"They've said it's there and they're going to implement it, but whether it's an accurate measure of children's learning and progress, the strong view that I'm hearing from teachers and principals is that it is not," she told APNZ.
Ms Mahuta said she did not buy that schools had such severe governance issues that they were not meeting achievement levels.
A spokeswoman for Education Minister Hekia Parata said the number of schools protesting national standards, by refusing to put targets into their charters, was now down to one.
Ms Parata said the ERO report referred to was from last year, and it was understood the last school not to include national standards in its charter would comply this week.