Firsthand and second hand teacher experience here. Decisions need to be made at the school level. Not federal, not state, not county or city (exceptions for rural, combined schools organizations, like the one I spent most of my school years). The district my wife and i work for, and we still have one child in, opened up all online back in August. Went a couple of weeks, then parents had the option to continue online or send kids into the buildings. Vast majority stayed online. District re-evaluated everything a few weeks later, discovered huge failure rates, mostly from online learners. Warnings were made, and shortly thereafter, many students were forced back into classrooms. As grading cycles have ended, parents are again offered the choice of online or face to face, and now, 2/3ds through the year, everyone is probably where they will be until the online option is revoked or something hits the fan and we all close up again.
I tell you all that to tell you this. My campus is a disciplinary one, we get kids who get in trouble. I'm on the middle school side, we have a whopping 11 students right now, total across 6-8th grades. High school is a little busier, but I don't know their exact numbers. These are very low numbers for us. We have had a couple of positive kung-flu tests and a few folks quarantined due to possible exposure, but nothing major. There is no reason for my school to close up or go all online.
My wife's school, pre-K/kindergarten building, on the other hand, is running a skeleton crew of teachers and staff (including janitorial staff) because of numerous positive tests, and people with shockingly similar symptoms whose test still come back negative. They need to close up for a couple of weeks, lysol bomb the whole building, but someone high up the chain (not sure how far) won't.
Teachers should be the same way. Individuals who are not in high risk categories and want to go to work should be able to, those who are worried can work from home. Union group think will just cause the students who are falling behind (and there are tons of those, this mess will definitely leave a mark on the education level of the US for several years to come, but that's another can of worms) to get further behind.