Dr. Maria Montessori developed the Montessori method in the early 20th century. The Montessori method allows children the freedom to explore their interests. In doing so, children learn about themselves, one another, and the world around them. Lessons and learning materials are designed to support educational development and inspire curiosity. 

This method emphasizes the individual child’s initiative and independence. Children move through different activities, called “work”, at their own rate of speed. Children learn first-hand while observing their peers. Observation allows children to learn from each other. 

• The method uses small sensory items like colored blocks to help the children complete a task. The method helps children discover their environment and world. 
• Montessori classrooms usually contain various ages. Teachers encourage each child to learn at their own pace.
• The Montessori method encourages children to develop leadership skills.

Sources:

http://www.montessorianswers.com/ami-or-ams.html

Association Montessori International (AMI)
https://amiusa.org/becoming-an-ami-school/

American Montessori Society (AMS)
https://amshq.org/Educators/Montessori-Schools/AMS-Accreditation

The International Montessori Council is another body that provides accreditation to schools in the U.S.:
https://www.montessori.org/imc-school-accreditation/