It's difficult to estimate. Of course, even with all this care, not everywhere is equally well ventilated. My room is wide open to the outside, but there are other rooms depending on central air and the room filter which may not be as well off. Trying to form policy on a room by room basis would be nutty.

> And is this benefit worth the difficult-to-quantify but very real cost of students being unable to see the faces of their classmates?

We do go outside quite a bit, and most students choose to not mask outside and thus see their classmates then. There's also the very real benefit of making many students-- and me, their teacher-- feel safer.

IMO the biggest cost is it's slightly harder to understand each other and we have a few more misunderstandings per day.