Did you ever read the Judy Blume book Blubber? It was no joke. It was about a girl who basically watches some popular girls pick on a chubby girl, and does nothing about it. And when you are in fifth grade, you most likely won't do anything about it, you will most likely keep your mouth shut, just like Jill did in this book. The book isn't about how much it sucks to be the fat girl being picked on (the girl they call Blubber isn't even the fattest girl in class- there is a girl way bigger than her.) And it isn't about the "cool" girl getting hers. It is about how fast things change. One day you are minding your own business, even considered cool, and the next day? It's you being picked on.
Are You There God? It's Me, Margaret is about a girl going through puberty and not knowing where to go with her questions. Margaret is desperate to get her period in this book, as are all of her friends, because they want to be women. They also want to wear bras and kiss boys and all that. I felt all of these things too- well, except for my period- I don't think I was all too thrilled to get that. Anyway, the book is written very well and really touches on the confusion of being a young woman. It also addresses religion. Margaret is being raised by a Jewish parent and a Catholic parent and is torn between religions. It is almost heavy.
If you haven't read these books as a pre-teen (I read them when I was eight- not a good idea) then get one and check it out. They still stand the test of time.