If a tree falls at lunch period

If a Tree Falls at Lunch Period by Gennifer Choldenko

First sentence: "This is lame but I'm actually looking forward to school this year, because every day this summer was like crap: dog crap, cat crap -- I even had a few elephant crap days. Trust me, it was bad."
Told in alternating chapters, the voices of Kirsten McKenna and Walker Jones tell the story of two kids and their middle school worlds colliding.
Kirsten world is falling apart, her parents marriage is falling apart, her best friend has dumped her for a more beautiful popular group, and her main way of dealing with this is eating.
Walker finds himself in a new world, where he's the only African American in the class and he knows that he can't mess this up (for his mom's sake).
Kirsten and Walk's worlds collide on more than one occasion - being late the first day of school, the teacher's missing wallet - but these are nothing compared with the family secret that Kirsten learns.

Read on.