There is a "real danger" that schools could remain closed until the summer, the Children's Commissioner warned as she blamed ministers for a "lack of planning".
Downing Street needs to "think creatively" about how to get youngsters back to the classroom and must "ultimately make something happen", Anne Longfield said.
Her intervention came as the Government came under mounting pressure from Tory MPs to explain why schools in their constituencies could not reopen after the February half-term.
In a new policy briefing on schools, Ms Longfield said: "Everyone recognises the necessity of reopening schools as soon as possible, but hope alone will not make it happen. What is lacking is a clear roadmap towards this. There is a real danger that schools will remain closed until Easter at the earliest, or even into the summer – not because the virus makes this inevitable, but because of a lack of planning."
She said that while the Scientific Advisory Group for Emergencies (Sage) could provide modelling of different options, it was the role of ministers to "think creatively about what those different options might be, explore all possibilities, come up with a plan and ultimately make something happen".
Ms Longfield set out a number of options for the gradual reopening of schools, including certain year groups returning sooner than others and children returning on a rota basis, meaning they take it in turns to come in on certain days.
She said reopening is "not a simple on/off switch", and that while it may not be possible for all schools to open before Easter, that "does not mean it is impossible" for some children to go back in some areas on a smaller scale.
On Tuesday, Gavin Williamson, the Education Secretary, came under fire for failing to appear in the Commons to answer Labour's urgent question on schools reopening. Instead, the schools minister Nick Gibb was pressed by MPs on what the Government's plan to reopen schools is.
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Siobhan Baillie, Conservative MP for Stroud, told the Commons that the reopening of schools should be treated as a "national emergency" and asked whether schools in Gloucestershire could open next month.
Felicity Buchan, the Tory MP for Kensington, added that the "majority of parents" in her area would like to see their children return to school after the half-term break, while Simon Jupp, the Tory MP for East Devon, suggested the option of reopening schools "on a regional basis" should be kept on the table.
Mr Gibb said a range of factors would be considered, including "hospitalisation rates and mortality, the rate of vaccination and the challenge of new variants", but declined to set out a precise timeline.
Speaking at a Downing Street press conference, Boris Johnson said he would "look at" whether children can return to the classroom on a regional basis, with certain age groups, such as those in primary school, returning earlier than others.
"We are working as hard as we can to get things open. We really wanted to keep schools open and we will want to reopen them, but we must do it in a way that is safe," Mr Johnson said.
"I appreciate the huge efforts that parents are now going to to teach their kids at home to look after kids who should be in school. School is the best place for pupils, and I know that the educational damage that we risk doing by protracted lockdowns."
On Tuesday night, a member of Sage warned that the decision on whether to reopen schools was a "judgment call" that could not be delegated to scientists. Dr Thomas House, a statistician at Manchester University who sits on the scientific pandemic influenza group on modelling known as Spi-M, said it was not for mathematical modellers to decide on "value judgments".
Speaking in a personal capacity, he told The Telegraph that "these aren't things where the science should be front and centre", adding: "Our job is to advise, not to decide."
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