Teachers have raised strong concerns over the government’s plans to mass test secondary pupils, warning that it will delay the reopening of schools and fail to catch asymptomatic carriers of Covid, as well as spreading “a false sense of security” among teenagers. On Monday, the government will reveal it wants schools to use controversial lateral flow tests to check secondary pupils for Covid-19 up to three times, before allowing them to return to the classroom in England on 8 March, the Observer understands. Millions of students will then be expected to test themselves twice a week at home, under the supervision of their parents, in a bid to catch asymptomatic cases before they can spread the disease to others at school. However, the NEU teachers’ union says many school leaders are “entirely unconvinced” that lateral flow tests are sensitive and accurate enough to pick up positive cases among asymptomatic young people, who typically have lower viral loads than adults. Mary Bousted, the union’s joint general secretary, said headteachers face a huge logistical challenge to set up mass testing in schools, and fear it will be time-consuming and pointless. “The idea that we could do three tests and open in one big bang on 8 March – that simply won’t be possible,” she said. It could easily take two to three weeks for the average secondary school, which has around 1,000 pupils, to carry out 3,000 tests, teachers estimate. School leaders who have already set up lateral flow testing regimes for vulnerable children and the offspring of key workers have “no confidence” they are fit for purpose, Bousted said. According to the latest NHS test and trace figures, just 0.31% of lateral flow tests conducted in the week ending 10 February found positive cases – a figure so low it is actually below the 0.32% “false positive rate” for these tests. “School leaders are telling us that they’re doing these tests and they just don’t get any positives. Their accuracy is very doubtful for mass testing. They’re not sensitive to small viral loads and secondary school pupils are much more likely to be asymptomatic [than older people]. So they’ll miss a lot of positive cases.” She said carrying out such inaccurate tests could be dangerous and give “an entirely false sense of security” to asymptomatic pupils who test negative. “If you’ve taken a lateral flow test which is giving you a false negative, then it’s all too easy to imagine that lots of teenagers will feel confident they haven’t got the virus and behave accordingly. “The danger is that these pupils start not to practise social distancing, hand washing and other protective measures.” Lateral flow tests “simply will not eradicate the virus” in schools: “School leaders don’t have any faith they are worthwhile.” She also warned it is highly unlikely that all teenage pupils will comply with the instruction to take a home test twice a week after they return to school, and that compliance will be difficult for schools to enforce. “How you police this is a nightmare. I taught teenagers for a long time, and I love them, but they have really quite clear views about their own bodily space. “Some will flatly refuse to stick swabs down their throat or up their nose – and I don’t think there’s much of an incentive for parents to ’fess up if their child won’t take the test. Or the child may tell their parents they’ve taken it, when they haven’t. ” On Friday, nine teaching unions, including the NEU, called for a gradual, phased return of children to school in England, warning that if sufficient time isn’t given to assess the impact of opening schools on transmission rates, it could trigger another spike in Covid infections. Professor Chris Whitty, the chief medical officer for England, is also said to be “very unhappy” with the idea of all 10 million children and staff returning to school on 8 March. “Headteachers are determined to open schools as rapidly as possible,” said Jules White, founder of Worth Less?, the grassroots headteachers’ group. “But we need to be trusted to make the right decisions for our local communities.” That includes the ability to operate a staggered start and, depending on local infection rates, use rotas which will allow children to socially distance more effectively in classrooms. “We want as many kids back in school as is safe for kids and staff.” A Department for Education spokesperson said: “We know schools, parents and pupils need clarity on plans as soon as possible, which is why we have committed to providing two weeks’ notice for them to prepare. “The prime minister is due to set out plans for schools reopening on 22 February, and pupils will return from 8 March at the earliest.”