Cast the Expert: Greg Townley as Number Three and Damien Walters as the Mogadorian warrior.
Also Alex Pettyfer as Number Four if you know how physically skilled he really is (watching Stormbreaker, made when he was just 15, may give you an idea).
Dawson Casting: Played straight as 24-year-old Dianna Agron, 22-year-old Jake Abel and 20-year-old Alex Pettyfer play high school students. 24-year-old Teresa Palmer as 16-year-old Six, too. However, it's averted with Callan McAuliffe who was 15 at the time of filming, and Greg Townley who was 14: their characters' ages.
Dyeing for Your Art: Alex Pettyfer dyed his blond hair brown for the beginning of the film. Jake Abel dyed his blonde hair brown for the duration of the film. Callan McAuliffe had his hair dyed darker for the film, but claims to have lost track of its original color because he's dyed it other colors for roles before.
Dianna Agron continued dying hers blond. Teresa Palmer literally ends up as the only actor without died hair. The Stinger? She's blond and her character had black hair in the book.
In the book, Sam's hair is also dark blond, as Callan McAuliffe's is, so he didn't need to dye it, the inverse of Teresa Palmer.
Money, Dear Boy: The author made no secret that he wrote the book to cash in on the popularity of the Literature/Twilight series and try to create a new hit franchise in its stead. That being said, it's much better than something supposedly written as an empty cash grab should be.