It isn't quite that bad, because the tests aren't independent. You end up with a few people who are disproportionately likely to test positive and can adjust appropriately your testing strategy for them.
And even if that wasn't the case-- you keep a few people home (them + close contacts) until followup molecular testing returns a negative. Yes, it's a big hassle-- you're "falsely" forcing 10% of the student body into remote learning, but probably better than remaining closed.
Yes. And then it’s not just one kid. It’s the entire class plus teacher. It would be a fire drill per day. And then they would need to take the tests every day until they are cleared. It’s not feasible.