These books were mostly really good, in my opinion!
Where the Mountain Meets the Moon by Grace Lin: I really loved this book. It was a short read with a great story. I think kids would appreciate the story as well as the moral while adults can find surprising depth, especially in the parents' side story. This book couldn't have a better message for our time: it is family that makes life happy, not prosperity.
Claudette Colvin: Twice Toward Justice by Phillip Hoose: I'm with Megan on this one... I really liked it and found it very informative. I think kids would like it to, especially 6th grade up. I think even younger kids (3rd grade +) would enjoy and understand excerpts. However, I don't LOVE nonfiction and therefore wouldn't read it for pleasure. Even though it was good.
The Evolution of Calpurnia Tate by Jacqueline Kelly: This was my least favorite of all of them. It was a tad on the slow side. It was definitely informative however, both as a historical and as a introduction to naturalism and the scientific method. I wish it had been better resolved; it wasn't clear whether or not Calpurnia really would get to be a scientist.
The Mostly True Adventures of Homer P. Figg by Rodman Philbrick: This one was my favorite! It was funny and I loved the characters. Also a great historical--this would be a great way to expose kids to the Civil War; maybe not the overall history but the meat of the conflict and how rough it was for the people who fought in it.
When You Reach Me by Rebecca Stead: I have very mixed feelings about this book. It didn't WOW me, although I mostly enjoyed it. I found the ending a bit too neat and cheerful for a book that dealt with such heavy topics, but I guess that's because it's childrens' and not YA. :) The book is a real page turner though.