Though I had very high expectations for this movie, I was very disappointed. One of the biggest discrepancies between the novel and the movie are the main focus or theme. While the novel focuses more on the morality of clones and attempts to bring the reader upon a horrific account of "normal kids," the movie focuses upon the romance aspect a little too much. Readers of the book will discover that many of the key interactions between Ruth and Kathy are missing.
In summation the movie takes a lot of liberty with the book's plot and I would highly suggest reading the book rather than just watching the movie