Children at low-decile schools are two years behind their peers in high-decile schools in both maths and health and physical education, a study shows.
It also suggested the curriculum expected too much of the country's 12-year-olds, with only about half performing at the expected level in either subject.
The National Monitoring Study of Student Achievement said only 41 percent of Year 8 children were performing at or above level 4 of the maths curriculum, the level they are expected to be at, and only 50 percent are there for health and physical education.
It said in maths, the age group was not doing as well as the curriculum expected on such problems as involving decimals, fractions and percentages.
In contrast, 81 percent of children in Year 4 were at or above curriculum level 2 in maths, and more than 95 percent were at that level for health and physical education.
The report, based on figures gathered in 2013, said children in decile 1-3 schools were doing worse, on average, than those at decile 8-10 schools.
It said at both Year 4 and Year 8, the difference in average scores was equivalent to the amount of progress expected over about two years of schooling.
The average scores for Maori and Pasifika children were lower than those of Pakeha and Asian children in both subject areas.
In health and PE, boys did better than girls on tests of movement skills and strategic action skills, but girls did better at sequences of movements.
Children from higher decile schools did better than those from mid and lower decile schools on these measures.
Minister addresses concerns
Education Minister Hekia Parata accepted there was a problem with teaching maths in New Zealand but said steps were being taken to improve the situation.
The minister said a number of reports had raised concerns about the matter.
"We do have a challenge in maths, which will be addressed by raising the quality of teaching, by ensuring that the resources that are available are shared," she said.
"And, actually, for any parent that is concerned about this, National Standards gives them the opportunity to discuss with their child's teacher how well they are doing at maths."
She said the Government was spending a lot of money on professional development for teachers, including for those teaching maths.