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.