Experiential learning!

Montessori equipment offers a set of development aids for children, the main function being to enable them to explore the world, to grasp it and to build.
The activities are divided into four practical areas: practical life, sensory, language, and mathematics. With the equipment the child has a visible and tangible error check which encourages self-correction: the child can see for him or herself whether an activity has been carried out correctly. By correcting himself, he becomes independent, can repeat the activity at his own pace and gradually develop his ability to concentrate.
This equipment allows the child to move from simple to complex, from concrete to abstract without having to obtain a teacher’s approval.

By placing the ruler on the board, the child learns and memorises the addition tables.