Parents and pupils in Wales will learn later if any classes will return for the final weeks of the summer term.
Education Minister Kirsty Williams said she will make a statement on Wednesday on the way forward for reopening classrooms following lockdown.
Children in England started back on Monday, although some schools have not reopened and attendance has varied.
The Welsh Government rejected plans to bring forward the start of the autumn term to August, according to unions.
The decision leaves the education minister with two other choices: Wait until September to restart, or reopen on either 22 or 29 June.
If classes do restart in three weeks, there is speculation different year groups will be prioritised.
In England, reception, Year 1 and Year 6 classes have been the first groups to return.
So far, the only Welsh pupils who have seen the inside of a classroom since the coronavirus lockdown have been children of key workers, or those deemed to be vulnerable, who have been attending school hubs to enable their parents to continue doing their vital jobs during lockdown.
Head teacher Jane Jenkins, of Moorland Primary in Tremorfa, Cardiff, has been running one of those hubs, and told BBC Wales it helped her understand what might be possible when more pupils return.
“At the moment, my thoughts are [on returning] at the beginning of July, increasing our provision and getting buildings up to scratch,” she told BBC Wales.
“The one thing the hub has shown is social distancing is impossible with young children. Under the age of six, children don’t have an understanding of it.”
But the return to school would look very different after lockdown, said Ms Jenkins.
It would be with smaller class sizes, no assemblies or group working, and no whole-school playtimes.
The teacher’s National Education Union in Wales has stated it wants to see classrooms return, but “not until it is safe to do so”.
Union officials said they hoped the education minister makes a “sensible decision”, taking into account the health and safety of learners and staff.
The NAHT, which represents school head teachers and leaders, said there had been positive dialogue with the Welsh Government.
“The Welsh Government have listened to what we have to say. School leaders have a set of skills and information which the government has drawn on,” said Ruth Davies, president of the NAHT Cymru.
She added that “nobody” wanted to see children returning to school more than staff, but that any next steps have to be done “carefully”.
The teaching union UCAC’s General Secretary Dilwyn Roberts added: “We want to see national guidelines which are clear and very detailed to ensure that there’s consistency across Wales and to ensure that all school environments are as safe as possible.”
- The announcement is being made during the Welsh Government’s daily briefing, streamed on the BBC Wales coronavirus live page at 12:30 BST, broadcast live on BBC One Wales from 12:30 until 13:00 and replayed on BBC Radio Wales at 16:00