Flowers for Algernon. Science Fiction, but with a soft edge.
The eponymous Algernon is a laboratory mouse who has undergone surgery to increase his intelligence by artificial means. The story is told by a series of progress reports written by Charlie Gordon, the first human test subject for the surgery, and it touches upon many different ethical and moral themes such as the treatment of the mentally disabled.
In 1958, Keyes was approached by Galaxy Science Fiction magazine to write a story, at which point the different elements of Flowers for Algernon fell into place. When the story was submitted to Galaxy, however, the editor suggested changing the ending so that Charlie ... lived happily ever after. Keyes refused to make the change and sold the story to The Magazine of Fantasy and Science Fiction instead.
A pivotal moment occurred in 1957 while Keyes was teaching English to students with special needs; one of them asked him if it would be possible to be put into a regular class if he worked hard and became smart.
I've read both the original short story and the novel. I think the short story is more powerful, but the novel is still extremely good. And, very depressing.