b'SensorialThe Sensorial Materials have been given many names: Materialized Abstractions, KeystotheUniverse,PathstoCultureThesemultipledenominationsare perhaps indicative of the enthusiasm the materials evoke in people who know them well. They are deceptively simple in appearance and totally satisfying to the developing child.The reason for the success and popularity of these materials is that they allow the children to undertake such activities as all children undertake, spontaneously. Given the opportunity, with or without specialized materials, children will sort things by size, shape, colour, touch, sound, temperature and weight. They will grade from dark to light, and from large to small. The Montessori Sensorial apparatus allows them to classify sensorial impression in an organized, orderly and scientific manner as well as they allow for individual work and for repetition.The Sensorial Materials are mathematically graded and limited in both scope and quantity; they isolate one quality only, keeping the remaining characteristics identical. This makes it possible for the children to abstract the concept made concrete in each piece of material, to name it, and then to apply it to the environment. Moreover, they have a built in control of error. Thanks to this control of error, the children acquire the habit of working independently, unafraid of making mistakes, becoming comfortable with the fact that errors are essential to the process of learning. And, incidentally, this establishes a tendency towards intellectual honesty. Nienhuis Montessori 17'