Assessment glitches reported in 180 schools
Northern Ireland's education minister has said up to 400 primary schools are experiencing problems with computer assessments for P4 and P7 pupils.
John O'Dowd said that between 200 and 400 schools have had trouble with the tests and that schools having problems should stop using the system.
Mr O'Dowd said that efforts were continuing to fix the problem.
In a statement, the Department of Education said that 180 schools had reported problems.
This figure was supported by the Council for the Curriculum, Examinations and Assessment (CCEA).
The Department of Education said that "in many cases these issues have been resolved and the school have gone on to successfully complete their assessments".
"Up to 400 schools have still to complete the assessments, however as schools should complete them before they have scheduled parental interviews, there may be many schools that have not accessed the tests as yet," it added.
Earlier, Mr O'Dowd said that "pupils at 500 schools have completed tests, but I didn't pay for 50% of a system I paid for 100%".
Many affected schools are in Lisburn and Paul Good from Lisburn Primary Principals Association has described the testing process as "a shambles".
"The technical problem experienced by myself and colleagues at neighbouring schools are servers crashing, screens freezing and tests going back to the beginning when we were assured that they could be saved and the children could complete them at a later time," he said.
"They have not been working very well for us at all."
The NI exams regulator, CCEA, confirmed there have been problems with the tests over the past three weeks.
The assessments were introduced in 900 primary schools in September.
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Sourcing and solving the problem remains a priority for all”
Earlier, the CCEA said that as yet, the "specific problem has not yet been identified".
In a statement CCEA said: "We are very sensitive to the impact that these problems may be having on pupils and teachers.
"Therefore, we have been advising schools who continue to experience technical problems to discontinue the assessments until this matter is resolved."
The new online literacy and numeracy tests were trialled in the spring and Mr Good's school, Meadowbridge Primary, was one of the 130 schools involved in the pilot.
He said that Meadowbridge had highlighted a number of problems during the trial but he claimed its concerns had not been taken on board.
CCEA's statement said: "Based on the information provided to date it is appears that the difficulties are related to system and network issues and include computers freezing or crashing and screens not displaying properly.
"CCEA and the assessment providers continue to work very closely with C2K and Northgate to investigate the problems as a matter of urgency and to determine the cause (or causes) of these issues."
In a separate statement, the service provider Northgate, said a "dedicated response team from Northgate, CCEA and C2K" has visited a number of primary schools affected by the issue to carry out tests on site.
"These investigations proved inconclusive as the problems previously experienced by schools were not replicated during the visits."
Northgate added: "Sourcing and solving the problem remains a priority for all."