Buses are also often older in more rural or less populated school systems and may not run in the extreme cold. Even my own car had trouble cranking a few days ago
In New Zealand it is very rare for school to be cancelled, in 2012 there was a tornado a few kilometers away and we still had to stay at school.
Only in the South Island does it rarely get canceled
I can confirm this living in the south. School's been cancelled due to a -20 degree windchill (there's no actual snow on the ground, but apparently these temperatures have been messing with my school's pipes).
I live in Florida and it was down to the forties. This is usually when everyone walks in to school with heavy parkas, scarves, hats, gloves, and hand Warmer's and still complain about the cold
Only in the South Island does it rarely get canceled