This method created in early 20th Century by Italian doctor, Maria Montessori tells us that kids from birth to 6 years old have the greatest capacity for learning. In that time they can build confidence to become independent by exploring and discovering. Everything in kids surrounding should be within his or hers reach, so they don't need help from adults. This theory mostly applies to kindergartens, but it can also be as effective at home, there small children spends most of their time.
As you now can imagine Montessori style furniture is child-sized furniture. Toys should be placed in open shelves, so not only you kid could reach them, that he or she can see everything openly, so there's no need dig for toys. The same goes to kids bed, it should be placed on a floor, easy to get in or out. The most popular "floor beds" are called house beds. It's a house framed bed with a grid in the bottom, for mattress.
Kids should be able to get their toys, books, clothes or snacks without a help from adult, so everything in Montessori styled bedroom should be in kids sized and in his or her reach. Don't forget about the safety, check if their is no sharp edges, etc. Help your kids become independent and self confident by making their room Montessori theory like. By the way, kids really love the small furniture and house beds.