I read this question Articles in real life where I saw a number of comments that said that it was typical of Turks, Arabs and Slavic speakers to say something like "Ich war in Schule" or "Ich gehe in Schule" because these languages lack the article model that German has.
But what about English, a Germanic language that obviously has different rules for the article usage when it comes to the word "school"?
I go to school. -> Ich gehe in die Schule/zur Schule.
I'm in/at school. -> Ich bin in/an der Schule.
School starts at 8 o'clock. -> Die Schule fängt um acht Uhr an.
In English, the rules are more or less clear for me. When we talk about school as an institution or education process, we don't usually use the articles. This doesn't seem to be the case in German.
So my question is, what are the rules in German?
Do you always have to use the articles in prepositional phrases?
(My guess is yes, because you have to differentiate things like "in der Schule" (wo?) and "in die Schule" (wohin?). That would be impossible if you used the zero article like they often do in English)
But then again, I managed to find an example where no article is used, for example:
Wir haben bis zwei Uhr Schule.
So when is it possible to use Schule without an artilce? Or is it only used in the fixed expression Schule haben?