I think live online class is not v. valuable for instruction. Use recorded videos for things that need audio or video elements. Use Zoom for camaraderie, smiling, fun, reconnecting. Have "office hours" by phone or--if needed--Facetime. Otherwise worksheets are good. No?

...Middle schoolers or HSers shouldn't have to check their email more than twice a day. The best thing they can get from email might be being forced to phrase a question they have coherently in written sentences.

...For HSers, I would think lectures would be best done as audio recordings.
One thing is that we should have on-demand online meetings be as rare as possible for kids, given family constraints on devices/privacy.