U.K. Prime Minister Boris Johnson urged parents to send their children back to school when they reopen in England next week, amid growing concern among some teachers and union officials that it’s not safe to do so.

“The risk of contracting Covid-19 in school is very small and it is far more damaging for a child’s development and their health and well-being to be away from school any longer,” Johnson said in a statement on Sunday. “It’s vitally important that we get our children back into the classroom to learn and to be with their friends.”

Pupils were sent home in the coronavirus chaos of mid-March, and most haven’t been back since. Without parents back at work, there’s scant hope of emerging from the continent’s deepest economic slump. And with Johnson’s government reeling from a succession of blunders in dealing with the pandemic, the stakes are high to get school reopenings right.

The country’s chief medical officers said Sunday that the Covid-19 fatality rate among those ages 5 to 14 is lower than most seasonal flu infections. There’s an “exceptionally small risk” of primary or secondary school age children dying from coronavirus if it’s contracted, they said.

‘Lasting Negative Impact’

On the other hand, “the risks of not attending school are significant,” Jenny Harries, England’s deputy chief medical officer, told the BBC on Monday. “We know that if children miss out on their education, particularly those in more deprived areas, that will have a lasting negative impact on their health and their life chances.”

International studies show that teachers are more at risk of contracting the virus from other staff than from pupils, the medical officers said. They also noted that a lack of schooling increases inequalities, reduces the life chances of children, and can exacerbate physical and mental health issues.

But the government can’t afford any missteps, with public trust running low over its handling of the exam grading fiasco in recent weeks. A spike in infections that forces schools to close would likely further hurt Johnson’s Conservatives in the polls.

The Department for Education says it has set out clear guidelines on staggered starts to the school day, minimizing contact between pupils, and social distancing for teachers. Scotland, whose academic year started already, implemented its own similar measures.

Schools Minister Nick Gibb, sent out on Monday to reinforce Johnson’s message in the media, said parents can be “assured that schools are doing everything to ensure that the schools are clean and that the risk of transmission is at an absolute minimum.”

“It is a moral imperative to get young people back into school,” he said.