That's the real issue here. As soon as someone tests positive, parents will start pulling their kids anyway. Half the school won't show up the next day if it's on the news that 4 people are positive in a school of 2,000... then what do you do?
How disruptive is that when every school with a case is closing, then reopening, some parents don't send kids, some parents have to send kids because they have no other option... then the way the rumor mill works in these suburban towns... probably only need a rumor of someone having COVID to pretty much shut a school down.
Much different than a factory or private business.