Maria Montessori believed there is a sensitive period for developing the senses.  Although the senses are an integral part of our lives, children during the early years, have the greatest potential to develop and refine them.  It is precisely this idea that demonstrates the purpose of Sensorial materials in the Montessori classroom.  The Sensorial materials are powerful tools, which allow a child to become aware of his unconscious impressions and bring those impressions in to conscious awareness.  Additionally, they enable the child to create a basis of order in his mind allowing for intelligent exploration of his environment. 
Montessori was influenced by the sensorial equipment designs of Itard and Seguin who used these materials while working with disabled children.  It was Montessori, however, who developed her own pedagogy to incorporate the materials to enhance the development of all children.  Use of the Sensorial materials aids children in developing and refining each of the senses.  Consequently, a better understanding of the world arises as the child is able to describe and articulate all that he observes.  Furthermore, the sensorial experiences create for the child an acute awareness of the beauty that surrounds him.

Color Tablets:  Third Box

The sensorial exercises designed by Montessori focus on each quality that can be perceived by the senses including size, shape, texture, scent, loudness, softness, matching, sorting, weight, taste, and temperature.  Furthermore, all of the senses are represented in the materials: The visual sensorial exercises enable the child to distinguish between similar and differing objects. These visual exercises can be divided into three categories including size, form and chromatic, or color.  Work competed with the Pink Tower or Brown Stairs enable the child to refine his skills in perfecting detection of size.  Exercises which enhance visual aspects of varying form would include work with the Geometric Solids.  The Color Tablets are a source for the child to perfect his visual skills regarding color.  The tactile sense is also represented in the Montessori Sensorial apparatus.  Work with the Fabrics lesson, Touch Boards and Touch Tablets enable the child to enhance, refine, and achieve sensorial awareness of touch.  Through work with the Baric Tablets, a child is promoting development of his baric sense and differentiating weights.  Likewise, the thermic sense is allowed to be exercised with the use of the Thermic Bottles and Tablets.  The olfactory and gustatory senses are also represented in the Montessori sensorial materials through the Smelling Jars, and Taste Bottles.  Additionally, an integral part of sense training in the Montessori setting is the development of the stereognostic/haptic sense.  Exercises with the Mystery Bag or Geometric Solids enhance and refine this unique sense.  All of the senses are represented in the Montessori Sensorial lessons.  Ultimately, they “guide the child to logical thought and [further] discovery,” of their surrounding world.

Pink Tower and Brown Stair extension.

An important factor of the Sensorial equipment is that they are scientifically designed.  Unlike Practical Life materials where the child has a frame of reference from the home, Sensorial materials are not familiar to the child.  This aids in maintaining an open mind about what the materials will teach. The purpose of the equipment is to focus the mind on one particular abstraction from the environment.  This distinguishing factor of Sensorial materials is called ‘Isolation of a Property.’  The color tablets provide an example of this factor by keeping size, weight, shape, and texture identical, providing the element of color as the isolated property.  Throughout the materials, the isolated property is non-adaptable, that is, the isolated concept is universal and can be used in any country or culture in the world.

Control of Error is also built into the exercises.  The student can see for himself when the material goes together correctly.  Likewise, he can see if a mistake has been made, analyze the problem, and solve it.  Interruption from the teacher or other adults is not required, in turn, building a higher sense of self-esteem and self-discipline within the student. 
Sensorial work is usually presented to an individual student or small group.  As the teacher, we must always assess the needs of the student and progress at the appropriate level and pace.  Participation during the presentation is encouraged should the student/s show interest.  Also, giving the child freedom to repeat an activity for as long as he wishes is an important factor in the learning process.  Presentations consist of two parts.  First, the child is shown how to handle the materials.  Secondly, the purpose or goal of the material is shown through the activity itself.  After the presentation, the teacher observes the child as he works with the materials.  Through careful observation, the teacher will note any mistakes and attempt to interpret them without intent for correction.  Most often, through the control of error, a child will discover their own mistake and adult intervention is not necessary. The teacher can always represent a lesson if she feels it is appropriate.
The Three Period Lesson is a vital tool developed by Montessori, who borrowed from Seguin, as an effective learning procedure for a student.  It is provided only after the student has had experience and is comfortable handling the material.   In the First Period, the teacher provides the terminology or answer.  The Second Period is the recognition stage where the teacher asks the child to show the answer.  Confirmation of knowledge is demonstrated in the Third Period and the child provides an answer on their own.  The Three Period Name Lesson is used not only with Sensorial materials, but in other areas of study as well. 
As a child’s senses are refined through use of the Sensorial materials, they are ultimately creating a better understanding of the world around them.  They become aware of beauty and aesthetics, better able to articulate and analyze information, and more prepared for intellectual activities.  A sense of pride and accomplishment develop as a child finishes his tasks and makes his own discoveries.  As teachers, we have a duty to provide children with a rich environment from which they can naturally develop into unique individuals with an appreciation and understanding of their world.