Instructional Dialogue

This is a work of thinly disguised (or sometimes entirely undisguised) nonfiction, written as a dialogue. Usually these dialogues feature a ~Mr. Exposition~, who either explains the topic to The Watson or debates it with a Straw Loser. In either case, ~Mr. Exposition~'s partner is supposed to be bringing up the objections or points of confusion that the reader might have.

Literature

 * Godel Escher Bach starts each chapter with a dialogue like this, between Achilles (The Watson) and the Tortoise (~Mr. Exposition~). They're modeled on a similar dialogue, "What the Tortoise Said to Achilles", written by Lewis Carroll (in which Achilles is more of a Straw Loser, though he comes round in the end).
 * How to Teach Physics to Your Dog by Chad Orzel is a quantum physics popularization featuring the author himself as ~Mr. Exposition~ with his dog Emmy playing The Watson.
 * Galileo's Dialogue Concerning The Two Chief World Systems combines the two forms; Salviati (~Mr. Exposition~) is given both a Watson (Sagredo) and a Straw Loser (Simplicio). The Pope thought Simplicio was a caricature of himself, which was really bad news for Galileo.
 * Plato's writings about Socrates are probably the Ur Example, and certainly the Trope Maker.
 * This is part of the concept for the Head First books. Even if the speakers happen to be abstract objects.
 * Neal Stephenson loves to deliver the Info Dump in his novels this way, in Anathem and Cryptonomicon in particular. Anathem even has appendices containing bonus Instructional Dialogue for people who didn't get enough of it in the main text.
 * Physicist George Gamow wrote a series of short stories, ostensibly about a man named Mr. Thompson but actually about quantum mechanics and relativity. Half of them are instructional dialogues where Mr. Thompson is playing The Watson to a ~Mr. Exposition~ generally referred to only as the Professor; the other half are Mr. Thompson's dreams about what would happen if the physics described in the dialogues was noticeable on a human scale.
 * Flatterland by Ian Stewart in large part is a series of dialogues between Victoria Line (The Watson) and the Space Hopper (~Mr. Exposition~) about various forms of geometry. It helps that they're traveling through all the geometric spaces that the Space Hopper is trying to explain...
 * Most of Sophie's World is taken up by a dialogue that summarizes the entirety of Western philosophy from the Pre-Socratics to Sartre.
 * David Weber

Video

 * The classic geometry video "Turning A Sphere Inside Out" is narrated like this.