Following her medical training, Maria Montessori began to develop her educational philosophy and methods in 1897, attending courses in pedagogy at the University of Rome and reading the educational theory of the previous two hundred years. While visiting Rome's asylums for the insane, during her schooling with a teacher, she used her observations of mistreatment of the children there to read all she could on intellectually disabled children, which lead to the creation of her new form of education. In 1907, she opened her first classroom, the Casa dei Bambini, or Children's House, in a tenement building in Rome. From the beginning, Montessori based her work on her observations of children and experimentation with the environment, materials, and lessons available to them. She frequently referred to her work as "scientific pedagogy".
In 1901, Maria Montessori met Alice and Leopoldo Franchetti (Baroness & Baron) of Città di Castello. They found many matching points between their work. Maria Montessori was invited to hold her first course for teachers and to set up a "Casa dei Bambini" at Villa Montesca, the home of the Franchettis in Città di Castello. Maria Montessori decided to move to Città di Castello where she lived for 2 years and where she refined her methodology together with Alice Franchetti. In that period, she published her book in Città di Castello. The Franchetti Barons financed the publication of the book and the methodology had the name "Method Franchetti-Montessori". Alice Franchetti died in 1911 at the age of 37 years old.
Montessori education had spread to the United States by 1912 and became widely known in educational and popular publications. As well, in 1913 Narcissa Cox Vanderlip and Frank A. Vanderlip founded the Scarborough School, the first Montessori school in the U.S. However, conflict arose between Montessori and the American educational establishment. The 1914 critical booklet The Montessori System Examined, by influential education teacher William Heard Kilpatrick, limited the spread of Montessori's ideas, and they languished after 1914. Montessori education returned to the United States in 1960 and has since spread to thousands of schools there. Montessori continued to extend her work during her lifetime, developing a comprehensive model of psychological development from birth to age 24, as well as educational approaches for children ages 0 to 3, 3 to 6, and 6 to 12.
Montessori education also spread throughout the world, including Southeast Asia and India, where Maria Montessori was interned during World War II.