The phrase back to school is hyphenated when it comes before a noun, thereby acting as an adjective. Do you capitalize birds names? do you capitalize species names.

Is Back to school correct?

Usually, “back to school” is a prepositional phrase. More specifically, “to school” is a prepositional phrase, modified by “back,” and the entire phrase “back to school” is a bigger prepositional phrase (in the same way that “hard to read” is an adjective phrase, and “very hard to read” is a bigger adjective phrase).

Is there a hyphen in back to school?

Back-to-school, back to school. For compound adjectives before a noun — that is words that are combined together to modify a noun — hyphenate whenever doing so might help the reader. “Buy back-to-school supplies when you go back to school,” AP advises.