The country's largest teachers' union has said it cannot imagine large primary school classes returning in September.
Health officials are not expected to allow schoolchildren to go back before the summer break.
The INTO said that when they do, large classes may need to be split - half in the morning and the other half in the afternoon.
General Secretary John Boyle said it is unlikely schools will be back to normal in September.
"I cannot imagine that children return in primary the way they were in on March 12 with 30 children in a classroom," he said.
"So the chances are that all the children initially anyway will not be back together in one group.
"That's going to pose very big challenges for their parents, for the children themselves and for their teachers."