Even when I was young, I thought it was completely insane that school buses didn't come with seatbelts of any kind. I heard all the excuses: school buses are so big they aren't necessary, kids won't use them, they'll only injure people, etc.
As far as I know, only six states today require safety belts in school buses. Six! Apparently, people still think that school buses don't crash, or that when they do the kids won't go flying. I can remember some of my bus drivers flying down the road and being scared at how fast we were going.
Take a moment to watch this crash test video, which shows what happens to kids that are secured using three-point belts versus those who are just sitting on the seats unrestrained. Imagine if any of the crash dummies were actual children and the kinds of injuries they would sustain.