When I taught in Cincinnati the cut off was 32 degrees and the playground had to be free of snow. The thought was many of the kids didn't have hats and gloves to stay warm in those temps so no one went outside. Of course, rainy days no matter what temps were indoors.

We drove by our neighborhood school last week, it was 30 degrees, snow on the playground, kids outside running around hatless, gloveless, a few without coats. I guess this is why Colorado is one of the healthiest (thinnest) states in the country.