Schools in England will remain closed until at least March 8, Boris Johnson has told MPs.
The prime minister dashed the hopes of millions of parents by announcing that schools would not re-open after the February half-term.
Instead ministers will try to begin reopening schools in the second week of March, if the current coronavirus vaccination programme remains on track.
Mr Johnson also pledged to set out a roadmap to lifting the latest lockdown after parliament returns from its own half-term holiday on 22 February.
At that stage ministers will be able to judge the impact of plans to vaccinate the top four most vulnerable groups by the middle of February.
Ministers have previously promised that schools would be given two weeks’ notice to allow them enough time to prepare to reopen.
Mr Johnson told the Commons: “The first sign of normality beginning to return should be pupils going back to their classrooms. I know how parents and teachers need as much certainty as possible including two weeks’ notice of the return of face-to-face teaching.
“So I must inform the House that for the reasons I have outlined it will not be possible to reopen schools immediately after the February half-term. But I know how frustrating that will be for pupils and teachers who want nothing more than to get back to the classroom.
“And for parents and for carers who spent so many months juggling their day jobs, not only with home schooling but meeting the myriad other demands of their children from breakfast until bedtime.”
Labour leader Sir Keir Starmer has called for all school staff to be vaccinated during the Februiary half-term.
He said his party would look at the details of how the education secretary plans to reopen schools.
Schools have been closed to all pupils except the most vulnerable and the children of key workers for three weeks.
Schools closed on January 5, just a day after Mr Johnson described them as “safe”.
Since then ministers have come under increasing pressure, including from Conservative MPs, to unveil their plans to lift restrictions.
Earlier this week schools minister Nick Gibb said any decision would be based on four things– hospitalisation rates, mortality rates, the “challenge” posed by the new variant as well as the progress of the vaccination programme.
Earlier this week Mr Johnson also appeared to play down the idea primary schools could re-open on a regional basis, where case numbers are low, indicating he preferred a national approach.