Earlier quoted context omitted.
The GDPR doesn't specify what you can't do with personal data, it specifies what you can do. Personal data is private by default; you can only use my data if it is explicitly lawful for you to do so. If you're not absolutely sure that what you're doing is in line with the GDPR, you shouldn't do it. That's by design, not by accident. The GDPR's fundamental principles are set out in article 5. You should collect the le…
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.
For a prison, it is. A school's purpose is to educate.