No question here. Four of the book's main characters are kids; the big suspense item is a statewide middle school Academic Bowl; the characters' conflicts involve moving to a new place, dealing with parents' divorce, starting a new school, being bullied, and trying to make friends.
Yeah, there's an adult plot, too—Mrs. Olinski's—but notice that she's the only main character who doesn't get to say anything in her own voice. Add in the heady philosophical themes about finding identity and going on journeys, and you have a book that's practically designed to win approval from teachers, parents, librarians, and awards committees.
From kids, though? You'll have to decide that for yourselves.