Earlier quoted context omitted.
The issue with the GDPR as worded and this ruling is that they remove the possibility of informed individual decisions. In this case it seems that all involved were informed and OK with it but that did not matter. I would also think that knowing where pupils are at all times is quite a legitimate aim for a school.
Everybody was informed and OK.... Except for the students they tracked, nobody asked them. Sure, they are still minors, and it's up to the parents to decide what goes and what not. But by law the parents in Sweden (and a lot of other places around the world) have an obligation to act in the best interest of their children to their best ability. I'd argue exposing their children to mass surveillance in school and face…
It's not clear (and honestly, not likely) that that was true either, but if it was:
> I'd have fine the parents a minor fine, too
This is child abuse, and should be prosecuted accordingly, including jail time.