Teachers' leaders have cast further doubt on a full reopening of post-primary schools in late August or September, saying it cannot happen on the basis of current public health guidance.
There is more optimism about a return of all primary pupils together, although Irish National Teachers' Organisation (INTO) general secretary John Boyle said it will only work if enough subs are employed to cover unexpected teacher absences.
Schools reopening dominated discussion at a meeting of the Oireachtas Covid-19 committee yesterday, a day after Education Minister Norma Foley published public health advice underpinning the return to classrooms.
The guidance covers the practical arrangements and practices to support a safe return of pupils and staff, but there is controversy over the key issue of social distancing.
The Health Protection Surveillance Centre (HPSC) advises that there is no need for physical distancing for pupils up to and including those in second class, but that a minimum one metre should apply for older students.
A one-metre rule would make it difficult for some schools to have all their pupils back in the classroom together.
Asked by Sinn Fein's Donnchadh O'Laoghaire about the prospects for full return, Teachers Union of Ireland (TUI) general secretary John MacGabhann replied: "I cannot answer as to when this will happen."
Mr MacGabhann said the union would engage with the Department of Education and other education partners "to ensure it can happen as safely as possible but it has to be done in a manner that guarantees safety for children, for parents and, I say without apology, for our members."
Association of Secondary Teachers Ireland general secretary Kieran Christie said he could not predict when a full return would be possible because there were too many variables that it did not control, the key one of which was social distancing.
He said under the public health advice published this week "many schools will not be fit to go back on full-time basis for all students".
As planning for reopening continues, much will depend on whether public health experts relax social-distancing rules.
The recommendation that no social distancing is required for half of primary pupils supports a fuller return in the primary sector, although the one-metre rule for older pupils may present challenges.
The INTO's John Boyle felt a full return should be possible, but called for supports to schools.