I desperately wanted to be Claudia in From the Mixed Up Files and Mary in The Secret Garden. I felt like I was living Mrs. Frisby's adventures in Nimh, wanted to be the 5th Musketeer and traveled with Gulliver all over the world.
But the 3 books that had the most impact on my life were To Kill a Mockingbird, Wuthering Heights and A Tree Grows in Brooklyn.
I clearly remember that I read Mockingbird when I was in 3rd grade and made it my life's mission to be Atticus Finch (failed miserably!). I don't necessarily think that I was too young for the story, but I obviously appreciated it more with each successive reading.
I don't know when I first read Wuthering Heights, but I do know that I have never felt such a kinship (?) with a book or an author. As soon as I read it, I then read a biography of Emily Bronte and found her poetry, and my love of that genre was born. To this day, I enjoy reading poetry even more than books.
A Tree Grows in Brooklyn opened my eyes to the way the poor suffered. I was a quite sheltered, middle class child who never had to worry about where my next meal was coming from. This book taught me about the lives of too many children, and I think I must have read it too early. I remember enjoying it, but I also remember going into a pretty deep depression for quite some time after. I would say middle school at least for my son.
And not a book, but I have to put in a plug for A Misummer Night's Dream and Romeo and Juliet, since they led to a love of theater, broadway and ballet.
I'll stop, because I could go on and on and on...