This is a novel I read back in high school and liked at lot at the time. I think it's a movie now. Here's a description:
Eva never really wanted to be a mother—and certainly not the mother of a boy who ends up murdering seven of his fellow high school students, a cafeteria worker, and a much-adored teacher who tried to befriend him, all two days before his sixteenth birthday. Now, two years later, it is time for her to come to terms with marriage, career, family, parenthood, and Kevin’s horrific rampage, in a series of startlingly direct correspondences with her estranged husband, Franklin. Uneasy with the sacrifices and social demotion of motherhood from the start, Eva fears that her alarming dislike for her own son may be responsible for driving him so nihilistically off the rails.