There may be such a shortage they are forced to take willing applicants with DWI history. Perhaps the applicants state they are reformed alcoholics who are not longer currently drinking or planning to drink and they take their solemn word on that. My understanding is that North of 30% of all current school bus drivers quit and leave the field every year, setting up an ongoing and persistent bum’s rush effort to fill the drivers seats by nearly any means.
The problem with being a bus driver is not driving the bus: it’s dealing with the passengers. School systems should be required to have a security officer of some kind on the bus, so that drivers can just drive.