Many of England's primary schools are opening on Monday, with rows continuing over whether pupils should return with the current Covid restrictions.
There is also uncertainty over how many classes could be closed after advice from a teachers' union that it is not safe for staff to be in school.
Head teachers warned of a "confusing picture" for parents and schools.
The Department for Education said switching to online teaching should be a "last resort".
Adding to the uncertainty, some individual local authorities have raised concerns about reopening.
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