I'm often accused of being anti-school and anti-teacher. In this case, I think this mother's expectations are unrealistic. I will concede this; it sounds as though the boy's teacher suspected he might miss the bus, which implies that there was an unusual circumstance. So, yes, the school may have had reason to believe the kid would miss the bus. But the teacher did tell him to go to the office if he missed the bus.
Maybe the school wasn't perfect here, but this doesn't appear to be negligence, from the facts we know. A couple of closing thoughts; obviously this mom called the TV station to make a big deal out of this. Two: WBAY recreates the boy walking in the cold. There was a day when this was a cardinal sin in TV journalism, without pointing out it's a recreation. It's subtle, but effective. And it is, in my opinion, unethical.