Former teacher here, watching the news and reading the runes, here's my 2p worth.
Easter is late this year, early April, which means that if kids go back on 22 Feb they will get a clear 5 weeks at school before Easter. This means that govt will be very tempted to give in to the perfectly understandable pressure from families who are struggling to cope.
We have a libertarian government that by instinct doesn't like telling people what to do, hence all the 'advice' and appeals to common sense, which in a minority of cases fell on deaf &/or stupid ears.
Up against that temptation will be the weight of medical opinion, which will no doubt counsel in favour of hanging on until after Easter in order to get the R number down to almost 0, and they will point to the (in their opinion) premature lifting of measures last Autumn as a mistake that should not be repeated.
So, as usual, it comes down to medicine v politics. No one votes for doctors, so I think we know what will win in the end. However, the politicians know that having nailed their colours to the mast of 'following the science' they will have to at least appear to still be doing so.
SO - I think we're in for a repeat of the phased return to school that we saw last year after Lockdown #1. The biggest problem in schools will be social distancing and space, so we will see big tents erected in playgrounds and on playing fields, extra support staff drafted in, and probably some rotation of days on/days off between year groups, as well as the previous 'bubbling' reinstated.
With all that in place, I think they will try to get Reception/Y1/Y6 back on 22 Feb, and probably Y10/Y12 in Secondary schools. They won't go for Y11/Y13 first because we already know that their exam grades will be teacher assessed, whereas hopefully the current Y10/Y12 will be taking real exams in 2022 and therefore they will want to get them back on track with their courses ASAP.
Once those groups are back I suspect they will then drip feed the others back as logistics allow, with the idea that all students should get 2-3 weeks of school before the Easter break. By this point the vaccination programme should have covered all school staff.
Finally, because the Summer term won't be interrupted by exams this year, expect a massive catch up programme with extra help for those who have fallen behind. Plans for this will already be in place in individual schools. And if travel is still restricted this summer, then either govt &/or schools may well decide to keep going until the end of July.
Here's hoping that 'normality' will then return to schools in September.