I think it has to be all or nothing too, especially for High Schools. I can just about imagine small primary schools managing on a reduced day - but that wouldn't help because the parents wouldn't be able to work for more than a few hours anyway, and that would cause more child care issues, and children would then mix with more people than if they were at school all day.
It definitely wouldn't be possible at our High School, we serve a really big catchment area, so a lot of the children are having to be using school buses - and they can't spend all day picking up and dropping off kids so some can come in in the morning, then others in the afternoon. And the timetabling/rooming for part time kids/staff wouldn't work. Which subjects do you prioritise? What about year 10, who are gearing up for GCSEs? How do they get their hours of subject teaching in on a part time basis for their chosen subjects?
It has got to be back full time. And because of that, I think it will September. Perhaps a phased return earlier for primary. And it can't be optional either, because how can you stagger teaching to suit this?
So, we have 10 classes for each subject. So, 2x set 1, 2x set 2, etc, down to 2x set 5. Each class has on average 28 kids in it. Logistically, we do this because we are open fully to serve the kids the best education we can (and this is about education, not child care). We can't possibly do this on a part time basis, and it wouldn't help the parents who want to work anyway.
So, unfortunately, although I'd be happy to go back to work full time tomorrow, I think it will be September. We would need to know now, this week, about a phased return after half term, in order to try and manage it. And we have been given no indication of that whatsoever.