DNiece (sensible girl, not a bullshitter), came home today a bit upset because her Art teacher? Has threatened to move her down to a low set which would therefore lower her English and Maths set.
In short, the Art teacher said if she didn't improve or start paying more attention, she'd move her down to set 4. DNiece is currently a Set 1 pupil which is top set and set via your standard of Maths and English.
DNiece asked how she could do that since Art was an option subject overall and Maths and English were not. Apparently the Art teacher said she didn't care and she'd move her down if she felt she was poor enough Art wise.
Surely this can't be a thing? 
She's always been brilliant at Maths/English and has great reports, genuine interest in
Those subjects and clearly does well marks wise. I just don't see how an Art teacher could move her for art and directly impact two core subjects.