I recently discovered the Replica series by Marilyn Kaye and it drew me completely in. Now I've got to find the other books in the series so I can keep up with what happens to Amy.
The topic of the book is very timely since it concerns clones, ethics in science and a clone's place in society. There's also the added intrigue of secret government agencies and mysterious agents (think X-Files).
Amy Candler thinks she is a normal twelve-year-old until her body and her abilities start to change. She finds herself becoming "perfect." Her hearing and sight improve. Her athletic ability becomes amazing and she even develops a birthmark that she never had before.
If that wasn't enough to put a girl on edge (though her friend Tasha insists that it's just "puberty"), strangers begin following her. Her mother starts to act incredibly possessive and she keeps winning contests that her mother won't let her collect a prize for.
Amy slowly pieces together her identity through some detective work and at the end of the book, has come to a truce (of sorts) with her mother.
Let me warn you now that you will become hooked on this series (there are quite a few books out now) and you will have to buy or borrow all of them before your curiousity is satisfied. They are also an easy read with concepts that younger readers will have no trouble understanding (friendship, competitiveness, parental control).