Sal Khan, who started Khan Academy in 2006, was a relative latecomer: "Flipping the classroom" was pioneered in part in the 1990s by Harvard physics professor Eric Mazur — and Dr. Mazur has said that it's a variation of law-school Socratic method that's been around (with pre-class reading instead of video) since the 19th century.

https://en.wikipedia.org/wiki/Flipped_classroom