I don't think all schools should close at all. We are tier 3 and our rates are 210ish per 100,000. Compared to 300ish back in October when we went to tier. No doubt this will change when new variant hits but for now it's safer than it was in October.
And with regards to Christmas mixing, even if families have broken the rules unless they have partied with 30 other familes, 5 days a week in one room for 6 hours at a time then they will have mixed much less than being in school for 2 weeks! It won't be this Christmas mixing that makes cases go up in school aged children and their families. It may have spread to grandparents etc which wouldn't have happened without Christmas. But who do you think will end up looking after children if they close schools?
And if they close them, when will they reopen? Are we to have another month off? Because nothing much will change with a month of vaccinations, the ecv will be done but not much of the general population and until a significant amount of the general population is done it will still circulate. And we are being constantly told its not just dangerous to the elderly and ecv, fit and healthy younger people end up in hospital too.
I have dd in year 12 and ds in year 2. Neither is in essential exams years but both benefit mentally, emotionally, physically and socially from being in school and being with their friends and teachers. I can homeschool ds if necessary, I'm fortunate enough to be at uni myself so homeschool myself and can do ds as well but most parents I know work and out of the home. In ds class we have a teacher, nurse, social worker who will obviously be key workers but their partners aren't so won't get a key worker place and will be either working from home around homeschooling or furloughed/unable to work. This all needs to be paid for, and while a magic money tree would be nice it doesn't exist.
That's not to say that some schools in some areas should open on Monday, I absolutely agree with those being closed. But if we close all schools everyone is equal and then it makes it more difficult to reopen I think. Closing in areas where rates are soaring is sensible but keep other schools open, if only to work on testing procedures etc.