There are reasons why school buses don't have seat belts, starting with the fact that a bench seat may be used by either two high school kids or three (or even four) elementary school kids.
Then, when I was riding school buses, there was what seemed to be a universal law that all school buses were grotesquely overcrowded. Figuring three bodies to a seat, which was not realistic, the bus I rode was supposed to hold 66 children--it was the same size as the one shown here...
...but a bus of that size would never have been used to haul only 37 students. A bus that theoretically seated 66 kids would routinely transport over 70. When the bus was close to the school, people were always standing in the aisle. Hard to tell kids to buckle up when their siblings can't even sit down.
School buses very rarely crash. This is fortunate, because when a school bus does roll, the only protection children have is the fact that they're relatively light, relatively unlikely to break the bones of anyone on top of whom they may land.
What should concerned parents do? If your children can't walk to school, consider homeschooling. The chance that a school bus will actually roll, as shown in Liz Klimas' report, is ridiculously small. This is a national headline news story because it's unlikely to happen again during the next twelve years. The chance that your child will be physically bullied, harassed, and breathed on by people whose parents thought they had colds or allergies but who actually have something worse, on the school bus, is...practically a guarantee.