Ministers are drawing up plans to stagger the return of children to classrooms in England from 8 March, with some year groups likely to be back earlier than others. Boris Johnson announced on Wednesday that he hoped “all schools will go back” on 8 March; but government insiders say a “big bang” approach, with all pupils returning at once, currently looks unlikely. “You could certainly see a situation where you started slowly, with pupils in particular year groups,” said an official. Younger primary school children, whose parents are having to provide intensive supervision for home learning, are expected to be high on the priority list, alongside secondary pupils in years 11 and 13, who should have been taking GCSEs and A-levels and are due to be assessed in the coming months. Johnson said no final decision would be made until the week of 22 February, when the government is expected to publish its plans for a gradual easing of the lockdown. The prime minister, who has told aides he is determined to be cautious, to ensure this lockdown is the last, overruled the education secretary, Gavin Williamson, who had pressed for an earlier opening date. The Guardian has learned that the government’s internal dispute over the issue began on Wednesday last week, with Williamson saying he wanted to announce by 8 February that schools would resume after half-term on 22 February. But in a sign of Williamson’s waning clout, scientific advisers cautioned that those dates could be over-optimistic, while the Cabinet Office and officials were able to persuade No 10 it would not leave enough time for schools to prepare. In a compromise, Williamson was allowed to announce the two-week minimum notice period for reopening. The Cabinet Office is also said to be close to approving the mandatory wearing of face masks in workplaces, which could lead to secondary school students having to wear them in class. Currently, schools and colleges have discretion over requiring face masks for students aged 12 and over in communal indoor areas. The government’s guidance is that wearing masks during lessons “should be avoided” because of the potential impact on learning. The National Education Union (NEU) is calling for secondary students to wear face masks in the classroom when they return – and for schools to use rotas and remote learning to reduce the number of pupils onsite at any one time. The NEU made the proposals as part of an education recovery plan aimed at helping to get students back to school safely. “Government must now initiate structured talks with education unions, based upon all available evidence, about how a phased return is best managed, irrespective of whether that is 8 March or not. School leaders can then begin making arrangements, confident that their time is not being wasted and that there is real potential for long-term solutions,” said Mary Bousted, the union’s joint general secretary. Labour shadow education secretary Kate Green has written to Williamson urging him to set out a “credible delivery plan” for returning more children to the classroom. She repeated her party’s call for teachers to be vaccinated during half-term; and suggested the creation of temporary “Nightingale classrooms,” to allow for more effective social distancing. “We need a national effort to get all children back into school with a credible delivery plan from the government which includes vaccinating school staff over half term and sets out measures to help make schools Covid-secure,” Green said.