Education Minister Peter Weir has defended the decision to allow NI schools to reopen on Monday, in order to "protect our children's education".
Mr Weir had said about one in every 20 pupils in NI was absent from school due to self-isolation or shielding in the week before half-term.
It was revealed in a written question from the MLA Chris Lyttle.
Schools closed on 19 October as part of tighter Covid-19 restrictions imposed by the NI Executive.
They are due to reopen on Monday 2 November and extra measures will be in place to allow pupils to return to classrooms safely.
That will include the mandatory wearing of face coverings for post-primary pupils on school transport.
Mr Weir said on Friday "schools represent a controlled environment".
He told BBC Radio Ulster's Good Morning Ulster programme: "There is nowhere in society which is entirely risk-free from this virus, let us be clear in relation to that.
"If we are going to send, on any longer-term basis, a third of a million children back into the wider community and believe that those children are going to be in a hermetically-sealed bubble in which there is no risk the big concern is what is happening outside of schools? That is where the big concern is.
"Are there risks anywhere?
"Yes there are, but those risks can be mitigated and reduced by way of all the actions in terms of good hygiene, in terms of taking all the precautions within society as a whole that we need to take."
Good Morning Ulster revealed on Friday that Mr Weir had been sent a letter by the principal of Braniel Primary School in Belfast.
The principal, Diane Dawson, said that while she agreed that schools needed to be open for all children, that should not be at "the expense of the safety and health of our school staff and community".
Mr Weir said "it is important that we protect our children's education that we ensure that the life chances of our children are actually protected by ensuring that children are back in school".
He added that parents had a "critical role" to play "in terms of both themselves and their children - trying to make sure that community transfer is kept to a minimum".
The Public Health Agency (PHA) previously said there had been 2,030 Covid-19 cases in total in about half of Northern Ireland's schools since the start of term.
However, a number of other pupils or staff can be told to self-isolate for 14 days if they are a close contact of a positive case.
Alliance's Mr Lyttle had asked the minister how many pupils had been absent from school under attendance code eight since the start of term.
According to Department of Education (DE) attendance guidance to schools, pupils are to be marked absent using code eight if they are "advised not to attend school following advice from PHA Contact Tracing Service".
Code eight can also be used if "a pupil chooses not to attend school or parent chooses not to send their child to school on the advice of a medical professional as the child is self-isolating due to a significant underlying medical condition".
Using code eight is "important to identify the number of pupils choosing to self-isolate due to Covid-19," the DE guidance to schools said.
Pupils self-isolating at home are still expected to complete work provided by their school or be taught remotely.
Mr Weir was unable to provide Mr Lyttle with the number of pupils marked absent under code 8 since the start of term, but was able to give the figure for the week prior to half term.
For the week commencing 12 October, 5.6% of all attendances were recorded as code eight by schools.
A further 2.4% of pupils were marked as code P - which is used if their school transport does not arrive or they "are not required to attend physically at school due to social distancing rules".
While Mr Weir was not able to tell Mr Lyttle exactly how many pupil absences those percentages represented, there are around 320,000 pupils in Northern Ireland's primary and post-primary schools according to DE statistics.
It is not clear how many school staff have had to self-isolate following contact with a positive case.