Teachers' unions have reacted with dismay after the government published new COVID-19 guidelines for secondary schools last night – just days before millions of pupils in England are due to return to the classroom next week.
One leader said there was a sense of "weary inevitability" about the plan, while Labour said the "incompetence is insulting".
If there is a local lockdown in an area with significant numbers of infections, schools could have to bring in a rota system for students who would spend two weeks in the classroom and then a fortnight studying online at home.
The staggered approach would be aimed at reducing a person's contacts, helping to limit the spread of the coronavirus and giving enough time at home for symptoms to show up.
The Department for Education guidance does not apply to primary school children, as scientific evidence indicates they "play a limited role in transmission".
The guidelines said schools should base their plans on a four-tier system so they respond to changing levels of coronavirus cases, and the approach prioritises keeping primary schools open.
Tier 1 will be the default setting where all pupils attend school full-time.
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And the extra measures should be introduced at the second tier if health and education officials believe infection levels are too high.
In this case, secondary school pupils would move to a part-time rota, where they would study at school for a fortnight and then study online at home for two weeks.
Tier 1 – Requires students in year seven and above, and staff, to wear face coverings in corridors and communal areas.
Tier 2 – Early years and primary schools will stay open, while secondary schools will move to a rota system, combining face-to-face and remote learning.
Tier 3 – Early years and primary schools will remain open but secondaries and further education institutes will go to full remote learning, with the exception of key worker children.
Tier 4 – All early years, primaries and secondaries will move to full remote learning other than for key worker children.
Teachers have criticised the announcement and its timing.
Geoff Barton, general secretary of the Association of School and College Leaders, told Sky News: "I think there will be a sense of weary inevitability about this, that we've been saying for a long time for weeks and weeks 'what's the Plan B?'
"What do we do once we've opened our schools and colleges, and welcomed children in, if there had to be a local lockdown?
"And that was responded to by the government as that it was a gross act of heresy even to question that.
"So here we are, right at the end of all that planning process, on a bank holiday weekend, children starting to come back on Tuesday, and late-ish last night the guidance suddenly arrives with some confusion over exactly what is implied.
"Of course we will respond to that and will make sure we do the planning that is necessary, but we could have been doing this weeks and weeks and weeks ago."