The Grammarians by Cathleen Schine

Wow, did this book just suck me in. First for its wit and humor, but then for its thoughtful and sentimental depth.  I loved the characters, I loved the structure.  The ending threw me for a loop.  Very emotional. I highly recommend this book!
Excerpt from the NY Times review (they like the book but not as much as I did!)

"...at the novel’s heart lies a profound philosophical question about the nature of the self, as Daphne and Laurel struggle to figure out who they are on their own and in relation to each other. Who gets to be the subject of their story and who is the object? Where does one person end and the other begin? When the sisters were babies, their mother worried that they were, perhaps too much, “each other.” Their father disagreed: “They were alike, two peas in a pod, but each had its own circumference. Daphne followed Laurel, a tiny acolyte. He wondered if Daphne would ever turn around and walk away. He wondered if Laurel would follow.” Their parents fear the girls will never evolve independently and also worry that they inevitably will."