"what's with no seat belts on school buses, anyway?"
An excellent question I, myself, have asked before. I do, however, have an answer to that old question.
The school bus seats are designed and spaced in a matter to prevent serious injury to children. They are designed to contain them like cubicles because the children are not likely to all be seated and facing forward. "Ah! But wouldn't seatbelts make THAT more likely?" you may interject. For some, yes, they would sit facing forward and belted into their seats. But more than likely they would not, they are children surrounded by their friends and peers and are relatively unsupervised. The other issue is that there is no way to ensure that the kids do buckle-up and remain buckled for the duration of the trip. Death and injury attributed to accidents for children riding in a school bus are extremely rare and it would also be cost prohibitive to retrofit millions of busses with seatbelts that would have a negligable effect.