The government is looking at "contingency plans" for if all England's children can't return to class in September, the Schools Minister admitted today.
Nick Gibb declined to say children would definitely return in full in September - saying only it was the government's "intention".
It raises the prospect of a possible fresh setback to school opening dates after unions warned the September date was impossible.
Boris Johnson has repeatedly insisted he wants all children in England to return to school from September.
But teaching unions say "the maths doesn’t work" under current distancing rules - which force schools to split pupils into 15-strong 'bubbles', doubling the number of classes.
The National Education Union has called on the government to use public buildings for extra classroom space and use "blended learning", with a mixture between home and classroom.
Mr Gibb was challenged today over whether the September date could become another U-turn.
He told Sky News: "Well our clear intention is schools will reopen for all pupils in September.
"We’re led of course by the science and the medical advice.
He added: "We are taking every step in a cautious way, we’re working with the school sector, we’re taking advice.
"And we give schools plenty of notice and time to plan for that reopening in September.
"Of course we’re working on other contingency plans, but the clear intention is we will have all children back in school in September."
A third of England's primary schools are still not fully open to years R, 1 and 6 despite being asked to do so since June 1.
And plans to reopen primary school years 2, 3, 4 and 5 by July were dropped when government officials accepted there wasn't enough space.
The growing crisis in education in England has seen millions of kids unable to attend classes since the unprecedented Covid-19 lockdown ordered in March.
Parents have been battling to homeschool youngsters amid fears some will fall behind their peers.
A report by University College London's Institute of Education found two million children have done less than an hour a day of schoolwork during the lockdown.
Today the government announced a £1billion catch-up package to stop kids being left behind.
Some £650million will be shared across state primaries and secondary schools over the next academic year.
And a £350million National Tutoring Programme will boost access to tuition for the poorest kids.
But the cash includes nothing for nurseries or further education colleges.
And is not clear about how much support will be given over the summer holidays because it is up to heads how to spend the cash.
Mr Gibb admitted the funding made available for schools will only start to be distributed from September.
Speaking on BBC Breakfast, he said: "The money will start to be paid in the academic year starting in September.
"Schools will know it's coming and they will be able to budget on that basis if they want to do things before September.
"But the money will start being distributed to schools, we'll have more to say about that shortly, from the next academic year, September."
The Government's education drive comes after the Mirror yesterday launched our Get Our Children Back To School campaign.
Experts say easing the two-metre social-distancing rule is key to fully reopening schools.
Speaking at last night's Downing Street press conference, Health Secretary Matt Hancock said: “We are working on what is needed to get all schools open in September, and there is a review into the current two-metre rule.
“But the two-metre rule is in itself a social distancing measure.
"Removing it has an impact in terms of the transmission of the disease, so we have to make sure in that review that we have the space and the virus is under control enough to be able to make the change and replace the two-metre rule, if that is the conclusion of the review, with something that then makes it easier to do things like have people together in schools.”