"Similarly to route duration,
doubling the route distance to reflect daily operating
distances, it is found that on average school buses travel
73.46 miles, with a 99.7% cutoff on driving distance of
154.46 miles."
That's double distance to cover both before and after school; they have a pause in the middle of the day to charge up again. There are battery buses on the market right now that do 155 miles, which is double all but 0.3% of routes out there. It also takes about an order of magnitude more power to run a motor for an EV than it does to run the heaters. If you get stuck in the snow in an EV at 50% charge, you can likely make it there through the night with the heater running.
The cold is a complete non-issue for this use case.