Because children abstract essential qualities from particulars things, their sensory development nurtures their mental growth.

Between the years of 3 and 6 children develop their senses; they turn their attention outward to the surrounding environment. It is during this period, Maria Montessori believed, that children should be exposed to stimuli that will develop their senses of sight, touch, hearing, smell and taste. Their sensory development lays the foundation in turn for their mental growth because children can — from birth — abstract from particular things their essential qualities.

To help children form these abstractions more accurately Montessori designed the Sensorial materials as series of objects grouped according to some physical quality they share, such as colour, shape, sound, texture, weight or temperature. The objects are designed to be attractive to children by dint of classic and harmonic proportions; to be manageable by their child-sized hands; and to encourage focus on some particular quality — sound boxes, for example, are all the same color so as to focus attention on the sounds they produce.

Children actively manipulate the objects in a series to compare and contrast them, sometimes with constraints to further encourage focus. Activities using the Thermic Tablets, for example, are performed blindfolded to help focus attention on touch. Children are thereby led to study qualities as such, whether length, breadth, height, colour, texture, weight or size. Montessori wrote in her book The Discovery of the Child:

Every series of objects, whether they produce sounds or represent different colours and so on, is graded so that there is a maximum and a minimum, which determine its limits, or which are fixed by the use which a child makes of them … When the two extremes are brought together they clearly demonstrate the difference that exists within the series and therefore determine the most striking contrast that can be achieved with the material.

The Sensorial materials help prepare children for further Life Skills activities. The Pink Tower, Geometric Cabinet, solid cylinders, the many matching games, the colour tablets, the Bells — Montessori wrote that they all help to “develop [children’s] perceptual abilities, visual and auditory discrimination, and ability to compare and classify, all powers necessary for written language.” Similarly the Touch Tablets are covered with various types of sandpaper to prepare for the sandpaper letters, while the Sound Boards enable preparation for the letter sounds.

The Sensorial materials also help develop motor activity. Montessori wrote: “A child is delighted to make and unmake something, to place and replace things many times over and continue the process for a long time.”

In designing the Sensorial material, Dr Montessori took inspiration from studies done by Jean Marc Gaspard Itard and Édouard Séguin on intellectually disabled children and from what she herself had used in psychological tests.