An international report on maths and science shows New Zealand 9-year-olds are lagging behind counterparts in countries such as England, Australia and the United States.
In science, New Zealand students scored just above the international average in the Timms Report, which looks at maths and science performance of Year 5 students in 36 countries.
While achievement levels have risen in recent years, the latest figures are a step back to the lower results recorded by the first Timms Report in 1994.
The Ministry of Education says the science findings are of concern and it is developing advice and support for primary school science teachers.
New Zealand students were just below the international average in maths, but recorded a similar score to the last survey.
The primary teachers' union, the NZEI, said science has not been a focus in primary schools.
Its president Frances Nelson said schools have concentrated on maths and literacy and science has struggled in a curriculum which she says is very broad.