She’s no Grinch about it, but Lynn Grewing is the principal who stole snow days. The early arrival of wintry weather in the Midwest this week gave Grewing an opening to test out a virtual class day at St. Cloud Cathedral high school in central Minnesota, having students whip out laptops or iPads and work from home. After a successful test run, Grewing declared Tuesday that students’ cherished snow days are a thing of the past—at least at Cathedral. […] Private schools like Cathedral—and, increasingly, some public school districts—across the nation are starting to use the flexibility technology provides to...