Hyphens, En Dashes, Em Dashes

Q. Do you hyphenate “student teacher”?

A. We follow Merriam-Webster and leave it open: “student teacher.” The term, in which “student” modifies “teacher,” is analogous to “student nurse,” which appears in section 2 of our hyphenation table (CMOS 7.89) under “noun + noun, single function (first noun modifies second noun).” Compare “writer-director,” in which the nouns represent two separate (and grammatically equal) functions.