Maths and education researchers are blaming ability grouping - seating children together based on their academic ability - for New Zealand's poor performance in an international maths test.
The average scores for New Zealand Year 5 and Year 9 students were the lowest in the English-speaking world, according to a study released this week.
The scores have barely changed over a series of tests since 2002, but the gap between this country's best and worst students has increased.
Glenda Anthony, the co-director of the Centre of Excellence for Research in Mathematics Education at Massey University, said ability-grouping children for maths appeared to be widespread and was a big part of the problem.
"What that's tended to do is to have your low achievers in a group that are often getting less than desirable opportunities to learn, in that they're getting a lot of basic facts practice and memorisation, and not developing those problem-solving skills that we want."
Professor Anthony said ability groups also reduced the amount of direct teaching that happened in a classroom.
"Our experience of being in classrooms is that often those groups that are working fairly independently. They're a lot of the time not achieving a lot of learning."
Professor Anthony said Massey University had great success with a project that got children to work together on maths in new ways.
"In the schools we have worked with, if we challenge this notion of ability grouping, teachers are just totally blown away with what children can do," she said.
"But it requires them to teach in a different way, it requires them to design tasks that are more open. It requires them to have children working in very collaborative ways."
David Mitchell, an adjunct professor at Canterbury University, wrote a book on evidence-based teaching and said streaming was bad, especially for children from poor families.
"Children in low groups, low streams, they are not given opportunities to learn equivalent to those in higher streams. It means that the children are exposed to lower order of the curriculum, they have low expectations placed upon them."
In Porirua, Corinna School principal Michelle Whiting said children did maths in groups, but they were not organised by ability.
She said that was good for the high-achievers, who were expected to explain their thinking on how to solve a particular problem, but was also good for those who struggled.
"It gives an opportunity for students who might not have the confidence to share their ideas to be included in a group where it's actually expected of them to do it."
Ms Whiting said the school was part of the Massey University project that encouraged active inquiry into how maths works.
"We're in our second year of that project and we are seeing accelerated learning in particular cohorts," she said.
"We've seen a huge increase in students enjoying maths and wanting to do maths and one of the best things for me is students being able to articulate their thinking and also to question other students."
Peter Verstappen, the principal of Wakefield School near Nelson, said his school gave up ability grouping two years ago in light of evidence that there were better ways to teach maths.
He said the results so far were mixed.
"Part of it is getting used to working in a different way. That means doing a lot of work on staff development and that takes time."
Mr Verstappen said New Zealand schools had long-standing strengths in reading and writing and there was a tendency to put those first.
"At the junior end of the school the priority tends to be literacy first, then mathematics. And so when school gets busy, of those core subjects reading, writing, mathematics, I think what does tend to happen is if we have to drop something, it's often the mathematics."
Education Ministry spokesperson Karl Le Quesne said schools should vary the groups that students were placed in.
"If ability groupings are used in a static way some children may never have access to parts of the curriculum or to experience the thinking of their peers," he said.
Mr Le Quesne said training teachers to teach maths better was a priority for teachers' professional learning for the next three to five years.
"We are also providing Teaching Support through the ALiM (Accelerated Learning in Mathematics) and MST (Mathematics Support Teacher). These provide support for teachers in mathematics to lift achievement of students working below and well below the standard in Years 1-8. The MST programme is specifically designed to increase the number of specialist maths teachers in primary schools."