The car thermometer read -3 (0F for readers elsewhere in the Anglosphere). All the schools in the area (at least all the public schools in slow-to-close Midland County and just about everyone else; I don't have a color-coded map of school districts handy to back up the "all") are packing it in for tomorrow in anticipation of -250F wind chill factors by tomorrow morning.
I don't recall schools closing for cold that much in the past. Snow and ice, yes, but not freeze-the-[kiester]-off-a-brass-monkey cold alone. We don't deal with negative temperatures in mid-Michigan too often, maybe once or twice a year in a bad cold snap, but we've gotten those quite a bit this winter.
The more macho and old-school folks among us might be of the school that if we went to school in zero-degree temperatures uphill...both ways...so can our kids. It gives them character...
...not to mention frostbite and damaged lungs. We might have had protective parents who made sure we had hats and scarves and mittens and thermal underwear (a.k.a long-johns) to brave those bitter-cold days; the modern kid is much more likely to ditch everything but the undies when he's out of sight of his folks.... if the parents are around to see them off at all.
Calling school off is a bit more protective that I'm use to, but so is the new rules in football and other sports on concussions. We know more than to just write it off as "getting your bell rung" and throw them back into the fray; we know the damage that concussions can do to folks, and the NFL is getting hit with a nine-heading-towards-ten-figure tab for past concussion damage.
We're also more aware of the damages of things like hypothermia and frostbite; in the old days, Frostbite was the first part of the name of the mythical town that Rocky and Bullwinkle lived in, not something to worry about while playing in the snow.
The kids might have a makeup day in mid-June that has them sweating in 85-degree heat. However, you can manage sunburn better than you can frostbite.