Yes, that's how it works in Alberta. It's particularly confusing because not all schools have the same academic calendar (e.g., most schools have a summer break, but a few have summer classes).
Unlike the sibling comment, there are no lights or indications of when school is in session. You must memorize the academic calendar of every school you drive past in order to know the speed limit. In practice, this means being conservative and driving more slowly in unfamiliar areas.
This is another example of something where, at least if you want to get all the way to completely correct operation, it's easier for an driverless car than a human. A person can't memorize the schedules of every school district they might pass, but an automated system potentially could. Of course something like Google Maps could solve this too, for both humans and Waymo.
Is it really such an imposition to simply drive at the posted limit at all times when passing a school? It only takes a few seconds even if you slow to a crawl.
Unlike the sibling comment, there are no lights or indications of when school is in session. You must memorize the academic calendar of every school you drive past in order to know the speed limit. In practice, this means being conservative and driving more slowly in unfamiliar areas.