The problem with that nearlyoldenoughtowearpurple is that the students in secondary almost always have individual timetables, certainly from year 9 upwards. So they wouldn’t be able to stay in the same classroom anyway. Possibly video link teaching might work for highly vulnerable teachers, but it requires tech that schools don’t have - most schools are really old buildings and struggle to even maintain decent WiFi.
I think that teens in part time would be better than any tech solution. If you halve class sizes it reduces the number of contacts and means that students get enhanced support. If you did week in-week off the week off would be consolidation of work in class, and it could be given as paper copies so students without internet wouldn’t be disadvantaged. It would also have the benefit of a weekend separating the two groups so there’s less likely to be cross contamination, and a teacher testing positive would therefore affect fewer students (current rules are contacts up to 48 hours before symptoms).
You can reduce the risk of teacher to student transmission by either saying teachers must teach from the front (no circulation) or by staff wearing visors. Ideally, of course, you could say that the vast majority of teaching should be from the front but teachers have visors so they can go over to a student if necessary. Teachers could wear gloves when touching books so we could mark work properly too. Visors and gloves would cost money, but I think government should be prepared to fund them.
Tech is good in a pinch, but there is nothing I’ve even heard of that properly replicates a classroom environment for the teacher-pupil dialogue which we know is vital to learning.