I was just looking into this myself! We run an outdoor education program from our farm in MO and I am a PDC graduate. I've been using Montessori materials with my own kids in our homeschool and taught for a little while in a private school that was Montessori based, but not a certified Montessori school. It's interesting because now I'm at this point where it seems like all of these loves of mine are converging and becoming one. I was thinking maybe I'd get a forest school certification and a Elementary I/II Montessori certification and make our outdoor education classes legitimate Montessori/ Forest School/ Permaculture classes. I wish there were more examples. I'm trying to formulate a concept of how it would all work.