The Prime Minister said it was "very, very important" for all schoolchildren to return on September 1 after unions suggested they could tell heads to keep schools shut if they did not consider them to be Covid-secure.
The latest data on the economy suggests a V-shaped recovery is still possible, with the services sector growing at its fastest pace for five years and Britons spending money on cars, consumer goods and eating out.
But the Government fears the recovery will stall unless people start going back to their workplaces in greater numbers.
Only one third of office workers have returned to their desks, according to a survey by Morgan Stanley, with huge implications for businesses such as cafes, shops and transport firms that rely on office workers for their trade.
Speaking during a visit to Cheshire, Mr Johnson said there were "real signs of strength in the UK economy".
He added: "Unquestionably, it will require people to have the confidence to go back to work in a Covid-secure way.
"It's also very, very important that we get all the schools back in September, on September 1, get all the pupils back into their schools. That will also be very, very important for getting our economy overall moving again."
Robert Jenrick, the Housing Secretary, urged people to "get out" and support local businesses in cities in order to prevent further job losses.
Asked whether he was worried that London is being "hollowed out", Mr Jenrick said: "Well, I am very concerned about London and city centres more generally.
"You are seeing people starting to go back into town centres and obviously using local shops in villages and rural areas, but many of our city centres are very quiet. We need to get back into them, using the Chancellor's Eat Out To Help Out scheme, going to visit the shops safely – it can be done.
"Shops and the hospitality industry are going to great lengths to make sure that they're following social distancing guidelines. Those of us that can do so need to get out and support them now – or else we will see, I'm afraid, further job losses and a loss of some of those fantastic businesses that we see in our cities."