I’m a little embarrassed to admit that even though I’ve been involved with Montessori for 11 years, I only recently heard of the delightful novel Understood Betsy by Dorothy Canfield Fisher. It’s a charming tale (much in the style of Little House on the Prairie) that brings to life the Montessori method in a creative way. 
Dorothy Canfield Fisher (1879-1958) was a major supporter of Maria Montessori’s theories and ideas, and helped bring Montessori to the United States. Her story cleverly weaves Montessori themes (multi-age classrooms; children working at their own pace; children connecting with nature) with the tale of a young girl, Elizabeth Ann, who leaves a drab life in the city for a colorful one in the country.
Stories are always great ways to teach; from parables to fairy tales, they can be more persuasive than the most eloquently reasoned arguments. People who are resistant to Montessori would probably benefit greatly from reading this novel. (The word “Montessori” is never mentioned, so it can be given stealthily to someone who is particularly anti-Montessori). Of course, teachers and parents who are already fans of Montessori will enjoy it too.
I also think it could easily be read by (or aloud to) kids from about age 8 on up. If they’ve been in Montessori for any length of time, most likely they’ll get a kick from hearing their own experiences meshed with this turn-of-the-century story.