Not sure how much seatbelts would've helped in this case... judging by the looks of it, at least some of the students were probably crushed.
Studies have been done showing seatbelts being a good thing on school busses, but of course, there will be accidents in which students will die because they couldn't get them off in time to get out, like in case of fire or being submerged.
But... like with cars and trucks, the greater good always goes with being belted in as dying
because you're belted in is 1 in 10,000 odds.
And kids being belted in would cut down on discipline problems somewhat also. Ask any school bus driver.