I was struck by the idiom school French, offered as a description of the kind of French that many people have in Australia. That is, limited in terms of vocabulary and appalling in pronunciation. School in this context means ‘rudimentary’.
It seems to be a formation that works with languages alone. We don’t say school maths or school geography. We are more likely to talk about veggie maths or basic maths. We don’t mention our school geography in the same deprecating way.
It is a little language oddity implying, as it does, not just rudimentary knowledge but the kind of stiff and stilted competency gained in the artificial world of the classroom as opposed to the fluency gained in the real world.