This is wrong. Too false positive and people will start ignoring the results. Thats what happened in the current climate. You need consistently good days otherwise over the long haul people will distrust and ultimately not follow.
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.