The issue in the US is not about safety near schools. School buses often have to go pretty far to drop evyone off, so most of their stops are not near the school. For route optimization they'll drop kids off on the opposite side of the road from where they need to be, not at a bus stop and not anywhere near a crosswalk. Also kids in the US tend to not be very mindful of how dangerous the road can be, so they are liable to run into the street unpredictably. To make sure kids don't get hit by a car that didn't see them, when stopping a school bus deploys a stop sign from its side that all drivers going either direction on the road must abide by (usually, there are exceptions, which makes matters worse). Drivers occasionally accidentally run these stop signs and very rarely intentionally run them.
Sounds more like a testing problem to me. Honestly I can't even remember if this particular rule was on the license exam when I took it. I know it because I put more care into remembering driving laws but many people don't.
Possibly an occasional refresher would help. I think it's just a weird thing to have. A roving stop sign that appears and disappears conditionally is going to have some people not see it (people accidentally run stationary stop signs on occasion), especially if you don't encounter school buses often. It's been maybe a decade since I needed to stop for one myself, I honestly cannot remember the last time.
