I would reserve Life As We Knew It for mature 7th and 8th graders, especially those intrigued with Hunger Games and Divergent. There is some romance involved and Miranda does mention her feelings about sex and becoming a woman. There is not a lengthy discussion about it but I can see some 6th grade parents being offended by this.
I had students from all grades requesting Raft and I understand why, now that I've finished it. If you like contemporary survival stories, this is one for you! As I was reading, I couldn't help thinking of the Open Water movies. Fourmile is a great book for boys, especially those who are missing their fathers. It's also contemporary fiction and topics include farm life and relationship abuse (not heavily mentioned but it is a possibility), as well as dealing with grief.
As I read Beholding Bee, I couldn't help but recall Water for Elephants during the carnival scenes. This one is historical fiction but it's a story of a girl trying to find her way in the world with the help of a mysterious woman in a floppy hat. I really liked the characters in this novel. Bee, or Beatrice, learns to run, to raise a dog and a pig, and to stand up for herself and friends with the help of some ancestors. I look forward to recommending these books to my students next year.