The Child’s first activity, involving numbers, in a Montessori classroom are The Number Rods. Another name for this activity is, the red and blue rods. They represent the quantities one though to ten.
“The teacher helps the child to count the alternating red and blue sections of each rod as he arranges them in a stair-like formation. The child calls the smallest rod One, the next rod Two, and so forth. The Number Two Rod is a unit, yet it is equal to two of the Number Rods.” A Parents’ Guide to the Montessori Classroom by Aline D. Wolf page 39
Through exploration with the material, the child also develops concepts in sequence of number, combinations of 10 and basic arithmetic. Rod 1 is 10cm in length. Each rod rises by an additional 10cm (cumulatively) until Rod 10, which equals 1 meter in length.