A snow day is the most random of childhood holidays, bestowed from above, with no way to plan for it other than having your sled on standby.

For many parts of the country, this has been an unusually mild winter, and snow days have been rare. But on Wednesday, families in Chicago, Detroit and places across the Midwest were tuning their radios, turning on their televisions and checking their cellphones to learn if the two to eight inches of snow in the forecast would close their schools.

But what constitutes good news in that moment is a matter of dispute: Children protest that a single snowflake is reason enough to cancel class. Parents insist they never got this many days off when they were young. And school administrators remind everyone that a snow day can cause disruptions that they are loath to unleash.

Those divides are the same today as they were years ago, but here’s a look at what has changed over time, from the frequency of snow days, to the effects of climate change, to online lessons making school inescapable.