I recently found out that John has never read the full Narnia series, just The Lion, the Witch and the Wardrobe. He doesn't know it yet, but I am going to get him at least caught up to Prince Caspian in time for the movie.
On a side note... has anyone ever read The Magician's Nephew last (instead of first)? In the UK The Magician's Nephew is numbered last in the series... I guess it's like a prequal. John swears the the UK ordering must be right since it was written by a UK author. Not bad reasoning... I'll need to look into that.