The phrase 'extra subjects' is correct and usable in written English.
You can use it when referring to additional topics that can be studied on top of the standard curriculum. For example, “Our school is offering extra subjects such as Spanish and robotics to students interested in expanding their knowledge.”.
Critical thinking and general studies are recommended to be extra subjects, on top of three or more A-levels.
Plus companies recruiting graduates sometimes use them as a streamlining tool, even though it isn't hard to game the system by picking up easy extra subjects or modules (general studies, anyone?).
They wanted us to work double the hours we agreed to and teach extra subjects besides English.
And while all of these "extra" subjects should receive more importance than they currently do, language learning deserves a swift boost to the top of our education priorities because it is a unique subject that helps students conceive of their world in a new way.
Already struggling, and facing new funding proposals set to hit schools with the poorest children the hardest, there's no way state schools can make space in the curriculum for "extra" subjects, so creative subjects like art, drama and design and technology are often the first to go.
The rest of the book follows the basic pattern of the earlier works, with chapters on soups, fish, meat, vegetables and sweets, with the addition of extra subjects relevant to Italian food, pasta asciuta, ravioli and gnocchi, rice, and Italian wine.
Tax and service extra; subject to availability.
Taxes extra; subject to availability and good for travel Monday to Thursday.
I took it as an extra subject because I needed to fill space; now I'm looking at a career in archaeology.
Cambridge accepts general studies and critical thinking A-levels only as a fourth, extra subject – but adds confusingly that it sometimes includes critical thinking in students' conditional offers.
In order to obtain a major in mathematics, I also needed to take an extra subject, which turned out to be chemistry.
