If there's an infrequent use of "mild to moderate" language and implicit or passing references to sexual activity, I'm unsure why this book would be rated so highly for sex and language. Violence? Of course violence is part of "Monster;" the story is about a young teenager on trial for aiding in a robbery which results in murder.
I rate this as appropriate for ages 13 and up not for any "controversial content," but because Myer weaves such a complex story, following the protagonist, Steve, as he struggles to understand how he's come to this point, his overwhelming trial, his dreams in life. Readers are left to figure out Steve's guilt or innocence; Steve himself must grapple with who he is versus what others see him as.
Though these questions are never explicitly asked, Myers' story encourages readers to consider how we view young, urban black men; how these perceptions are internalized; justice; how a life (potentially) derails. "Monster" is a quick read that will draw in reluctant readers with its mixed journal and screenplay-style narrative, but be warned: it not only entertains (because let's face it: it's just a darn good story), it also gets kids and teens to think.