Positive Covid-19 cases have been reported in 64 separate schools in NI among staff or pupils in the first two weeks of the school term.
The Department of Education (DE) revealed the figure to the Stormont Education Committee on Tuesday.
Up until Tuesday 8 September, DE had been notified of 88 positive cases in 64 schools.
More than 300,000 children returned to classrooms in the first week of September.
The data on how many pupils and staff have been advised to self-isolate as a result is held by the Public Health Agency (PHA).
Adrian Murphy, from DE, told the committee that a number of schools had been in touch with the department about positive cases.
“We know how many schools have been in contact with us and in contact with the Education Authority where they have had positive cases reported,” Mr Murphy said.
“The department itself does not hold data on the actual number of positive cases, that data is held by the PHA,” he said.
“They hold all the testing data and the information in terms of whatever pupils or contacts of pupils would then be confirmed as a positive case,” he added.
“All we know at the point when we are managing this system is that we have been contacted by a number of parents and a number of schools where we have closures.
“Yesterday that was 88 reports into schools of a positive case in 64 education settings.
“You need to be mindful that that is out of 1,300 educational establishments so 64 is actually a very, very small proportion,” he said.
‘Only test if they have symptoms’
Mr Murphy did not specify how many cases were in primary, post-primary or special schools.
A number of schools in Northern Ireland have sent groups of pupils home to self-isolate for 14 days following advice from the PHA.
Mr Murphy also re-iterated that children should only be tested if they have symptoms of Covid-19.
The SDLP’s education spokesperson Daniel McCrossan said the numbers would “cause concern”.
“We need to be assured that we have a robust testing and tracing operation capable of meeting the increased demand that we’re going to experience in the coming weeks and particularly as the cold and flu season begins,” he said.
“We need to make sure that there’s a mechanism for ensuring rapid testing of these cases in our schools to minimise disruption and keep the entire school community safe.”
However, the department also said that pupil and staff attendance rates at schools in the first full week of term were above 90%.
According to John Smith from DE, overall pupil attendance rates in primary schools were 92.8% while in post-primary schools they were at 94.6%.
In special schools, pupil attendance rates were 87.2%.
Some 96.3% of teaching staff had been in school from 1 September while 97.3% of non-teaching staff had attended, according to the department.