Most people don't drive past schools at excessive speeds. The speed limit should be set such that most people are naturally inclined to drive at that speed anyway, given the context of that stretch of road, not set to the fastest speed which outlier maniacs drive at.
The speed limit should be set given the context of what should be safe for the area with the road, and the road design should encourage drivers to drive at that speed.
If its a stretch of road where we don't want cars going more than 30mph, we should set the speed limit at 30mph and design the road, so people tend to go about that speed. Not have a stretch of road where we want people to go 30, build a road people feel comfortable driving 55 in, and then decide "welp, nothing we can do, just change the speed limit I guess."
