Likely nothing. Look at Florida for a decent example of what’d happen at scale if we left schools open. It’s been fully open, 5 days a week in person, since the start of the most recent school year last September. The state as a whole has done better at dealing with the virus than other similar sized large states. It also has a wide range from dense urban to light rural populations.

It’s not that you don’t have any mitigations. It’s that you tailor them to the problem. Florida did have lockdowns for senior centers and that likely lowered the overall death rate given the skewed mortality stats.

So why did they open, but not CA or NY? I’m sure cozying up to the teacher’s unions at the very least factored into those states’ Governor’s decisions.