Schoolchildren have got worse at basic arithmetic skills since the introduction of new teaching methods designed to lift the country's poor performance in maths.
The Ministry of Education figures show the number of Year 8 (12-year-old) children who could answer a series of simple multiplication questions correctly within four seconds dropped from 47 per cent in 2001 - the year new maths teaching methods were introduced - to 37 per cent in 2009.
Critics of the new methods highlighted the findings after Education Minister Hekia Parata described the performance of New Zealand children in an international test as "extremely concerning".
Our 9-year-olds finished bottom equal among developed countries in the 2011 Trends in International Mathematics and Science Study (TIMSS) published last December, with half the students unable to add 218 and 191.
Private maths tutor Huw Wainwright of Can Do Maths said the ministry's own figures from the National Education Monitoring Project (NEMP) showed "about one-third of students hitting high school not knowing their times table, with division knowledge even worse".
The NEMP report also noted a drop in performance among Year 4 (8-year-old) students in quick recall and understanding of basic addition and multiplication between 2001 and 2005. It said Year 8 students did much worse in difficult long multiplication questions because they were using the new methods.
The changes were introduced after a political outcry at New Zealand's poor performance in the 1995 TIMSS test and the creation of a national taskforce to improve maths and science teaching.
The ministry's 2001 response, known as the Numeracy Development Project, was supposed to lift student performance by giving primary teachers more confidence in maths. Critics say it has instead confused teachers, children and parents by presenting multiple alternative problem-solving strategies but neglecting basic knowledge.
Margi Leech, director of maths tutoring company Numicon NZ, said the new approach had many good points but was too abstract for many children and teachers.
She was not surprised that research at one Auckland school found 90 per cent of 9- and 10-year-olds were at risk of failing.
Ministry of Education group manager Pauline Barnes said she would be concerned if teachers were not promoting knowledge of the basic facts because their instant recall was critically important to problem-solving, estimation and other key mathematical processes.
Ms Parata said the results showed the need to use information effectively to change teaching practices, especially for slow learners.