In the montage of Beaver reading the book, he appears to be reading it backward. For example, when Wally picks up the book from the sleeping Beaver, Beaver appears to be about halfway through the book. A couple of shots later, as Beaver's walking in his bedroom, he appears to have just started reading the book.
When Beaver reads his book report about "The Three Musketeers" based on the 1939 film, some of the events that he describes do not occur in the film at all.