Math operations include addition, multiplication, subtraction, and division. All these operations require full understanding of quantities on a concrete level before moving to the abstract level of performing these operations mentally. So the first exercise introduced to the child to prepare him for these operations; is the “Number Rods”. The ten number rods are graduated in length from 4 inches length for the shortest one, to 40 inches length for the longest one. The different four inch sections are alternately colored red and blue and can be counted on each rod. So , each rod consists of distinct countable units, united together to represent a number. This overcomes the difficulty of adding one unit after another in a sum total. “The fact that a group is enlarged through the addition of a unit, and that this increasing must be considered; constitutes the chief obstacle for the children of three and a half to four, in learning how to count.” Maria Montessori, The Discovery of the Child, page 263
Several activities are done with the number rods. All of them are activities of moving and joining. One time the child builds them next to each other starting with the shortest and ending with the longest, and another time, he builds them on top of each other. All this joining and moving is an introduction to arithmetic. Then the “Sand Paper Numerals” are introduced to the child, to teach him their names and how to write them. Later on the child learns to match the card to the corresponding rod, which “forms the basis for a lengthy task which a child can continue by himself. The sums of the rods can be written so that they correspond to the numbers.” Maria Montessori, The Discovery of the Child, page 265
Two other objects are used to help the child begin arithmetic; The “Spindle Box”, and “The Cards and