Rules by Cynthia Lord
Twelve-year-old Catherine just wants a normal life. Which is near impossible when you have a brother with autism and a family that revolves around his disability. She's spent years trying to teach David the rules from "a peach is not a funny-looking apple" to "keep your pants on in public"---in order to head off David's embarrassing behaviors.
But the summer Catherine meets Jason, a surprising, new sort-of friend, and Kristi, the next-door friend she's always wished for, it's her own shocking behavior that turns everything upside down and forces her to ask: What is normal?