Standardised testing scores for thousands of Australian students have been delayed because of concerns with comparing written and online tests.
The Australian Education Union claims Education Minister Simon Birmingham was repeatedly warned results from different NAPLAN test formats could not be compared and that scores could be delayed up to five weeks.
The results were due to be released to parents and schools on Wednesday by the national assessment authority.
It's understood some state education heads had issues with comparing scores for the new online tests, sat by one in five students in years three, five, seven and nine, with the traditional handwritten assessments.
AEU boss Correna Haythorpe said it was a "disaster" for the testing system and repeated the union's earlier call for online tests to be scrapped.
"NAPLAN online is fundamentally flawed and must not be implemented," she said.
A spokesperson said the results would be released shortly.
"NAPLAN results are usually provided to schools, parents and students from mid-August to mid-September, depending on each state and territory."
Education bosses are expected to meet with the Australian Curriculum, Assessment and Reporting Authority in Canberra on Wednesday.