Boris Johnson will tell MPs that all pupils in all years can go back to the classroom from March 8 it is being reported this evening.
The preview of the prime minister's announcement to Parliament tomorrow, briefed to political journalists, is likely to provoke opposition from teaching unions.
They had joined forces on Friday to warn that a "full return of all pupils on Monday 8 March" would be "reckless"
The big bang approach to school openings is controversial because of fears from teachers' leaders that it "could trigger another spike in Covid infections, prolong the disruption of education, and risk throwing away the hard-won progress made in suppressing the virus over the course of the latest lockdown".
There have also been concerns from some school leaders that conducting Covid testing on pupils will not be feasible without a phased return.
It is understood that secondary schools will be allowed to stagger the return of year groups within the first week back beginning 8 March, to allow Covid testing.
The prime minister is set to outline the finalised back-to-school plan in a statement to the Commons tomorrow (Monday) afternoon.
He has stressed the need to relax restrictions in a “cautious” manner, saying that the government would make decisions based on the latest data at every step.
Ahead of his Commons address, Mr Johnson said: “I’ll be setting out a road map to bring us out of lockdown cautiously.
“Our priority has always been getting children back into school which we know is crucial for their education as well as their mental and physical wellbeing, and we will also be prioritising ways for people to reunite with loved ones safely.
“Our decisions will be made on the latest data at every step, and we will be cautious about this approach so that we do not undo the progress we have achieved so far and the sacrifices each and every one of you has made to keep yourself and others safe.
“We have therefore set four key tests which must be met before we can move through each step of the plan.”
Ministers will assess the success of the vaccine rollout, evidence of vaccine efficacy, new variants and infection rates before proceeding to the next step.
The tests are currently being met, Downing Street said, allowing the first relaxation to take place on March 8.
Restrictions will be relaxed step-by-step across the whole of England at the same time, Downing Street confirmed, due to the current uniform spread of the virus.
Mr Johnson will chair a virtual meeting of his cabinet tomorrow (Monday) morning to discuss the plan, and then unveil the details to Parliament in the afternoon.
He is expected to host a Downing Street press conference at 7pm tomorrow alongside key advisers.