My wife, who is a big potter fan, told me they take traditional classes as well, but they are shown off screen as they aren't interesting to the story.
Pretty sure they explicitly talk about those kind of classes in the books. They don't have scenes in them, but I remember Ron and Harry complaining about arithmetic, or mathematics, or something like that.
"Arithmancy" is what they call their math disciplines and it's mentioned a fair bit in the books, though understandably never really shown in the movies.