Girls Like Us by Gail Giles

Giles, G. (2014). Girls like us. Somerville, Mass:  Candlewick Press.
This book is the winner of the Schneider award.  The Schneider Family Book Awards honor an author or illustrator for a book that embodies an artistic expression of the disability experience for child and adolescent audiences.
Quincy and Biddy are both graduates of their high school’s special ed program, but they couldn’t be more different: suspicious Quincy faces the world with her fists up, while gentle Biddy is frightened to step outside her front door. When they’re thrown together as roommates in their first "real world" apartment, it initially seems to be an uneasy fit. But as Biddy’s past resurfaces and Quincy faces a harrowing experience that no one should have to go through alone, the two of them realize that they might have more in common than they thought — and more important, that they might be able to help each other move forward.
Another book with the similar theme of the mentally challenged is My Louisiana Sky by Kimberly Willis Holt.Tiger Ann Parker is smart in school and good at baseball, but she's forever teased about her family by the girls in class. Tiger Ann knows her folks are different from others in their small town of Saitter, Louisiana. They are mentally slow, and Tiger Ann keeps her pain and embarrassment hidden as long as her strong and smart Granny runs the household. Then Granny dies suddenly and Aunt Dorie Kay arrives, offering Tiger Ann a way out. Now Tiger Ann must make the most important decision of her life.