Leviathan

Alek is a recently orphaned heir to the Austro-Hungarian throne. His countrymen have turned on him and are hunting him down.

Deryn is a girl pretending to be a boy so that she can sign up for the British Air Service.

Alek fights on the side of the Clankers, a steampunk style of machinery, and Deryn fights on the side of the Darwinist, using modified beasts. It is the beginning of WWI, and as unlikely as it may be, both Alek and Deryn cross paths and have adventures and grown together.

Leviathan is perfect for middle school aged readers. It reads in difficulty and sci-fi/fantasy as Harry Potter and the Percy Jackson series. This would be a great follow up book for readers who love those two series. Sci-fi and steampunk enthusiasts will love this alternative history novel.

Chapter 6: Fiction Genres for Adolescents

As fanciful and disbelieving as the world that Scott Westerfield creates in Leviathan may be, he artfully weaves the two main characters in such a way that you grow to love each of them. Sci-fi and fantasy writers create and develop characters who grow to be real to [the readers] (Woolls pg. 80) 

Westerfeld, S. (2009). Leviathan. New York: Simon Pulse.
Lesesne, T. (2003). Making the match the right book for the right reader at the right time, grades 4-12. Portland, Me.: Stenhouse.