After working with subnormal children as a psychiatrist at the Univ. of Rome, Dr. Montessori was appointed (1898) director of the Orthophrenic School. There she pioneered in the instruction of retarded children, especially through the use of an environment rich in manipulative materials. In 1901 she left the school to embark on further study and to serve (1901–7) as lecturer in pedagogical anthropology at the Univ. of Rome. The success of her program at the Orthophrenic School, however, led her to believe that similar improvements could be made in the education of normal preschool children, and in 1907 she opened the first case dei bambini [children's house] as a day-care center in the San Lorenzo district of Rome. The success of this venture led Montessori and her followers to establish similar institutions in other parts of Europe and in the United States, where the first Montessori school was established (1912) in Tarrytown, N.Y.

In 1929 the Association Montessori Internationale was established to further the Montessori method by sponsoring conventions and training courses for teachers. By this time, however, interest in Montessori education had declined in a number of countries, especially the United States, mainly because of opposition from those who felt that the method was destructive of school discipline. The Montessori method experienced a renaissance in many American schools during the late 1950s, and in 1960 the American Montessori Society was formed.