This happens fairly frequently in Vancouver Canada, although it's not from regular school commuting (we do have special school busses), but rather from daycamps that find public transit to be the best solution vs. renting a private bus; but also — perhaps surprisingly — school field trips, which seem to often find "just get on a city bus" simpler to arrange than getting the public schoolbus system(?) to get drivers to work a special spot shift hauling kids to who-knows-where.
Interesting, where I grew up school children could not use public transport (while at school at least). We had our own bus system (which was superior to the public transport) and sometimes used private for-hire buses.
