The Labour Party's education spokesperson says New Zealand's ranking has fallen in the OECD's reading, maths and science tests of 15-year-olds.
Chris Hipkins says New Zealand has done worse in all three areas of the Programme for International Student Assessment.
Results from PISA's testing of students in 2012 are embargoed until 11pm on Tuesday.
Mr Hipkins would not blame the National-led government for the fall in New Zealand's performance, but says its policies are making things worse.
New Zealand has consistently ranked in the top group of nations for reading and science and just outside the top in maths since PISA began in 2000.