A reader sent me an email today wondering it there is any research about using Montessori for adults. Great topic! I’m just going to brainstorm here, and we’ll see what happens. 
First: what did Maria Montessori think of adults and how they learn? We already know about the learning cycles most evident in ages 0-6 and 6-12: the 0-6 period is a time of intense internal growth and the 6-12 period is a time of reaching out and learning about the outside world. Montessori believed that those two types of growth periods repeated over and over again throughout a person’s life. If you look for those patterns in your own life, you can usually find them.
Another observation is that adults often seek out “hands-on” hobbies and tasks just like kids do. Someone who wants to unwind after a long day at the office may put together a model airplane or knit a sweater. Older people, particularly, want to return to the earth by gardening or building with wood. This tactile stimulation satisfies a need in adults just like it does in children. There is satisfaction in work, exploration, mastery, repetition, and perfection.
Should Montessori principles be used with adults? This is another question entirely. There are companies that use Montessori principles (or at least what they think are Montessori principles) to design their workplaces. Certainly companies like Google, which have free-flowing office spaces, creative toys available for employees, and non-linear organizational structures end up being some of the most creative companies out there (and it probably isn’t a coincidence that Google’s founders, Sergey Brin and Larry Page, both attended Montessori schools as children).
But should Montessori methods and materials be used in adult education? My personal opinion is that it’s not always effective. The reason is that the goal of adult education is different from that of child education. The child is constructing the adult; the adult is adding to an already-existing completed personality. The difference between these goals should not be underestimated.
One great example is the Montessori training. Sure, during the training we had plenty of time spent in hands-on experience with the materials. It was much easier to learn to present the checkerboard by trying it ourselves rather than reading about it or watching someone else do it. But when it came to theory, lectures were the best way for us to learn. We didn’t need nomenclature cards for the tendencies of humans, or impressionistic charts to understand the balance of liberty and discipline. Again, we were adding to our body of knowledge, not refining our senses the way a child does.
One place that Montessori materials and methods can be used with adults is for rehabilitation. In cases of stroke or dementia, the adult is now reconstructing the person just a like a child constructs his initially. Even then, the actual Montessori materials may or may not be used; the therapy may simply be conducted in a Montessori-style manner.
I don’t know of any definitive studies showing that Montessori works (or doesn’t work) with adults. Most definitely the principles of respect and self-directed learning, and hands-on activities last a lifetime. Whether Montessori-style learning materials are needed for adults is doubtful. Perhaps some of you have experience with this?