The things people keep posting about death rates are missing the point, IMO.
If schools can't reopen without teachers getting ill, they won't stay open for very long. We saw this in the week before lockdown. Unless there is really quick testing, if we are still sticking to the 7 day self isolation rules, a cough going around a school will quickly shut it again.
For me, before schools reopen, we need really robust testing in place, and we need clear guidance on what happens if there is a case in school. This isn't necessarily about safety, it's just about having schools open as viable places that won't suddenly shut again!
To answer the questions in the OP: from a secondary PoV
How would social distancing be adhered to?
Students stay in classrooms in small groups- with desks spread out. Teachers move to students. To have enough space, obviously we'd have limited children in. Packed lunches to be eaten in classrooms. A shorter school day, with less breaks, potentially.
How about drop off and pick up?
Staggered arrival and home times- students not allowed on school premises before their arrival time. These would be geographical, due to buses, rather than age based. For us, the school entrances are a real crunch point during the morning/afternoon, so I think this would be the only way forwards.
How would classrooms operate?
Students spread out at individual desks (we do have classrooms where we could do this with say 10 students). Limited chances to get out of their seats. No sharing of equipment, which would be tough for the ones who turn up without a pen.
How about lunchtimes and breaktimes?
For secondary, I think we are better off shortening the school day and minimizing these. Either that or staggering them throughout the day, and having kids out only within small groups. Kids would have to go outside, rather than using the limited inside space available.
What about after school childcare provision?
As a secondary school, this doesn't really apply. I don't think after school clubs would be running. For primary, I could see this being possible with very limited numbers only- or a much higher staff/child ratio which will push the prices up.
What about staff who are sheidling?
Stay off, obviously, and provide work/support for children who aren't in school for whatever reason. Could also work on the gained time tasks for the year.
What about children who are sheilding?
Again, obviously they should stay off- with work being provided/supported by specific staff.
What about staff who have family members who are sheilding?
I think this is where it becomes a really tricky grey area. I don't think my school could operate if all people with a sheilding family member + vulnerable + pregnant stayed at home- even with a limited number of children who are in. It is bloody tough and will probably have to be decided on a school by school basis.
It is obviously not as easy as saying "just let them quit" especially if they teach a shortage subject. (Not that we should be saying "let them quit" anyway, but if we lost a good maths teacher we would probably struggle to replace them- and I don't just mean short term).
Should only some children go back? Who should they be and why?
For me, from a safeguarding and educational perspective, I think having all years getting some face to face time would be good. In an interim period, expanding the number of "key worker" children in school might not be a bad thing. I'd rather have one year group in each day of the week, instead of, say Y10 all the time.
If we are told we can only have some year groups in, I would actually have Y10 +7 back first because Y7 are least able to stay home alone for long periods. I reckon Y12 are managing with online learning better than other year groups. Our Y12 is quite small and classes would be easy to socially distance BUT once you have sixth formers in, you have to deal with issues like study periods etc which is an added complication.