Daniel Keyes, Flowers for Algernon (Millennium SF Masterworks S)

Charlie Gordon had learning difficulties and he has been chosen to be the subject of an experiment that is supposed to increase his intelligence. The story is told through his "progress reports" and along the way, he becomes a genius and ends up exploring the subject of women more than he would have in his "natural" state. Interestingly, we also see some flashbacks into his memories that, put together, tell some of the reasons why he was the way he was.