For example, the one I'm currently reading The Sign of the Beaver is about a boy in the wilderness of Maine trying to survive. Definitely a BOY book.
By contrast, the book I finished reading yesterday, A Ring of Endless Light was definitely a GIRL book. The main character is a girl and she's trying to sort out her feelings towards three different boys.
That isn't to say that all books with girls as the main character are girl books and ones with male characters are boy books. In fact, I can think of one popular book with a boy as the main character that seems to be equally liked by both boys and girls
And also this book:
I don't know if it's the fantasy aspect or if it's because there's an ensemble cast of characters but I see girls and boys picking up both of the above series.
This all started when I was lamenting to my husband about how in grade school, I was forced to read "boy" books all the time. I was a good reader and had no problems reading stuff on my own but I really hated most of the books that we read in school. My husband pointed out that in his day (back in the 70s), he had to mostly read "girl" books and the pendulum seemed to have swung the other way by the time I was in grade school in the 90s. His theory was that girls are more apt to read "boy" books than boys are to read "girl" books. While I don't think that it's really fair to the girls, I would say that it's an accurate assessment.
What makes a "girl" or "guy" book?
Boy + Dogs + Hunting = Yeah, it's a boy book (but I like it actually)
Boy + Hawk + Survival + Woods = Another boy book (I like it too)
Girl + Puberty + Other girls + School = Girl book
Girl + Boy + Sparkly Vampires + Romance = Girl book
My solution to this whole debacle? How about some student choice? Let the kids pick what they want to read from a list. Would have saved me a bunch of headaches in grade school (for the record, I was a straight A student, I just despised reading class when we weren't reading something that interested me).