School buses are designed in a compartmentalized fashion, that is the seats are close together with high backs, which keeps passengers relatively restrained in a crash, even without seat belts. The NHTSA has spent a fortune studying this, and has found that adding seat-belts doesn’t increase the safety of school buses enough to warrant a full refurbishment or re-design of buses.
School buses also have a much lower center of gravity, so in a crash with a normal vehicle, the passengers are much higher up, and less likely to be affected by any damage. Of course, this doesn’t take into account rollovers of buses, which is thankfully pretty rare, also because of the design.
You also have to take into account to the young age of children who are on the bus. Enforcing the seat-belts would be impractical, but even worse, many younger children may struggle to get themselves out of the belt in the rare event of a serious crash, meaning they are unable to escape through an emergency exit without additional help.
There is only an average of 6-10 deaths of school children in school buses each year, and while that’s tragic, it would be impossible to get that number to 0, even with seat belts. Statistically, school buses are 70% safer than a car in terms of getting your child to/from school, and full-size buses are literally the safest vehicles on the road.
It should be mentioned that smaller buses do have, and are supposed to require, seat belt use in most places in the US.
– CletusVanDamnit