I recently read Rules by Cynthia Lord and absolutely loved it! The book is about a girl who must deal with an autistic brother but it's also about friendship, relationships between kids, and belonging.
Rules won the Schneider Family Book Award in 2006. That award is for books that help readers understand and accept people with disabilities and it certainly deserves the award. (One of my books, Signs of Trouble was nominated for that award in 2010, but didn't win.)
I love Cynthia Lord's book and hope lots of middle grade kids will read Rules.