Montessori Associations
There are a number of associations that offer Montessori training. However, I would only reccomend becoming trained through AMI (Association Montessori Internationale) or AMS (American Montessori Society) training centers. The word "Montessori" is not patented and therefore ANYONE can throw the word Montessori into their school (for children) or training center (for adults). It's very unfortunate, and can lead to a lot of confusion. There may be other training programs that have worked for other people, but I am unfamiliar with them. AMI and AMS are two well-known, well-established and respected associations. Links to these websites are under Montessori Associations on the right hand side.
AMI and AMS
So, what's the difference? I can't quite answer this question, and it's one about which I still have some questions. The pedagogy appears to be the very similar (I've seen some small difference), though the training formats are different. Please, if you have further insight, leave it in the comments. I should also note that I am AMI trained, and therefore have more information about AMI. I chose to become AMI trained because of the reccomendation by my former teacher and because it was started by Maria herself.
AMI and AMS programs offer training in A to I (Assistants to Infancy/Toddler), Primary and Elementary training. While I was writing this post, I stumbled upon this post from Educating for Life that very nicely outlines what an AMI Primary and Elementary training course looks like. I am unfamiliar with the format for AMS, although I know that are internship programs. AMI training programs also offer the option to obtain your Masters in Edcuation through Loyola College.
Click here for info on AMI training centers
Click here for info on AMS training centers
Click here for LOCAL info on the Washington Montessori Institute/Loyola College
Where Can I Teach?
With an AMI diploma, you can teach at any AMI, AMS or unaffiliated Montessori school. You can also teach internationally, hence the "internationale". With an AMS diploma, you can teach at any AMS or unaffiliated school.
As for teaching in public Montessori, it starts to get a little bit confusing. In DC, you must be AMI trained. It was part of a stipulation when the programs were put in. However, other states/districts hire both AMI and AMS.This is a neat little tool from Jola Montessori (Public School Montessorian) that lets you search for schools in your area. This is a bit broader than the one on the AMI or NAMTA website, because it includes Public, Charter and Independent Schools.
If anyone has any other questions, I'd be happy to answer them! Also, I'm hoping some of those AMS-ers out there, can fill in the holes that I don't know about.