Well, I guess it was desperation ;-) We had bought the materials for Education students to become familiar with this approach and I used them in one class to explain Montessori's ideas. I was concern with the critical thinking issue at the same time, so I just notice my students would order the pieces right but were not able to give an account of their process... That was the beginning. After that, I just needed to teach them the names of their intelectual steps, and then started to sequence and compare... It works beautifully also with medicine and Arquitecture students!
I actually teach Critical Thinking to my colleges students using preschool materials: constructions, figures and forms are great to teach logic, classifying, ordering, planning, analyzing, etc. In a visual way, they learn to decode a piece of information in its smallest parts, to conect the dots, to order and argument, to build critical reasoning with adequate support... Since the y are not familiar with Thinking skills training, because there is nothing like that at Spanish schools, making it visual helps them much to understand what is it about. Montessori's materials are specially great for this.