A secondary teachers union say the Covid situation in schools is "quite worrying".
Up to 12,000 children are restricting their movements due to being a close contact of someone with Covid 19.
That's based on around 700 primary schools and 500 secondary schools reporting a Covid-19 case.
At primary school level, each case has an average of 15 close contacts, and around four in secondary schools.
Kieran Christie, General Secretary of the Association of Secondary Teachers in Ireland, says more data will emerge over the next week or so.
"We've been assured that people who are in schools are operating in an environment where the Delta variant, because of the mitigation controls in place, won't be transmitted throughout the school.
"That's been seriously tested, and we're operating on the basis of the assurances we've been given.
"We'll certainly know more in the next 8-10 days."
