"Montessori" is not a trademark or a franchise: any institution can hang a shingle over its door and claim to offer a Montessori education.
So how can parents tell whether a Montessori school is authentic?
Doctors have the AMA; architects the AIA; engineers the IEEE. Surely there's an organization for Montessori teachers who combine a doctor's awareness of neural development, an architect's careful artistry in construction (albeit for children rather than buildings), and an engineer's keen, logical approach to problem-solving.
There is: AMI, the Association Montessori Internationale. Founded by Dr. Montessori herself in 1929, AMI is the most diligent of the various Montessorian organizations in ensuring that Montessori schools and teachers are both well-grounded in the basic principles of the method and ready to carry those principles forward in the modern educational world. AMI offers teacher training and conferences, approves the production of Montessori materials and books, and, through their AMI-USA branch office, accredits schools.
Of over 100 schools in the Houston area claiming the Montessori name, The Post Oak School is one of only four recognized by AMI-USA (of just over a dozen in the state of Texas).
To receive AMI Recognition, each classroom in the school must have:
Schools receive an outside consultation from an experienced AMI teacher every three years, verifying that these requirements are met and offering workshops and suggestions to help school staff further refine the program.
Every three years, trained consultants evaluate AMI schools at each level as a part of the ongoing school accreditation process.