Many more children than the Government expects may fail national standards in reading, writing and maths.
A comparison of the Progressive Achievement Tests (PATs) - developed by the Council for Educational Research - with the national standards indicates higher failure rates than the Ministry of Education anticipated.
In the Year 8 maths standard, the ministry had projected 50% of children will fail, but a comparison with PATs indicates a 65% failure rate.
A senior researcher at the council, Charles Darr, says either the standards are harder than expected or the comparison of PATs with the standards was too tough.
Mr Darr warns that children might be discouraged from further maths study if they are failed against the Year 8 standard.
Some principals have warned that parents will be surprised when above-average children fail to meet the standards.
The primary teachers' union on Monday questioned the relevance of national standards in reading, writing and maths.
New Zealand Educational Institute president Frances Nelson says it is not clear the standards have any relevance and there is no evidence they are at the right level.
However, the Ministry of Education is sticking to its predictions for pass rates, saying the worst rate will be 50% for the Year 8 maths standard.
The Council for Educational Research has warned teachers to be careful how they use the tests when making national standard judgements.