I was employed as an educator, from 2002 to 2007, in a public high school in a small town until I could no longer work because of my physical disability. I also drove a bus route before and after school. As an educator, I can follow your opinion and logic. It would seem like a no brainer to use seat belts for safety on a school bus. Afterall, that's why we wear them in our vehicles. We have a greater chance of surviving a crash, right? However, these crashes are unpredictable. During my fourth year, three teens decided, with their parents permission, to make a run to the big town for some take out lunch. It started to rain on their way back. The driver who had a reputation of always driving too carelessly, drove too fast, in order to get back before the bell rang. On a infamous curve, he lost control and the truck barrel-rolled. The driver and the middle passenger were ejected through the back window, while the third passenger was caught in the truck. No one wore a belt. And to make this long story short, all three students were released from the hospital later that evening. But their surviving does not inspire me to not wear my belt. That's my personal experience from the teacher perspective.
From the perspective of a bus driver. . . seat belts would not be effective. Its not about the money or the kids tearing them up or using them on each other. For a seatbelt to be effective, it has to be worn. In order to make sure belts stayed buckled, a driver would have to stop each time a student unbuckled themselves and that would happen constantly. It is not legal just to park your bus on the side of the road. It could cause an accident.
There are federally mandated rules in place for students safety on the bus, of which, the number one rule is to 'stay in your seat'. It seems simple, but it took me half of a semester to drill it into the heads of my passengers and luckily my transportation supervisor was behind me. If parents and school districts would back the rules for safe bus-riding, then your students would be safely tranported without the use of a seat belt.