Montessori’s ideas were well received internationally, and Montessori societies to promote her work were formed in many countries. However, Montessori maintained tight control over the use of her name and insisted that only she was able to give authentic training in her methods. In 1929, she founded the Association Montessori Internationale (AMI), "to maintain the integrity of her life’s work, and to ensure that it would be perpetuated after her death." AMI continues to train teachers using materials and presentations developed by Montessori and her son, Mario Montessori.
Montessori societies were established in the United States and in several European countries during Montessori's lifetime, but teacher training and authenticity remained under Montessori's control. In 1960, after a dispute with AMI, the American Montessori Society (AMS) was formed. According to AMS, "The two organizations have since reconciled their differences, and now enjoy a collegial relationship of mutual support and respect." AMS trains teachers and states on its website that "AMS is the largest Montessori organization in the world." Other smaller organizations offer training as well, and there is an ongoing controversy in the Montessori world about what constitutes authentic Montessori.
In 1967, the US Patent Trademark Trial and Appeal Board ruled that "the term 'Montessori' has a generic and/or descriptive significance." Therefore, in the United States and elsewhere, the term can be used freely without giving any guarantee of how closely, if at all, a program applies Montessori's work.