Montessori Subtraction Table

OVERVIEW OF THE MATERIAL:

• 1 chart running from 1 to 18, with the first nine numbers in blue and the others in red, and
• the line of the ninth column is the same colour as the first nine numbers, blue, unlike the other lines which are all red
• a box containing beige rods from 1 to 17
• a box containing blue rods from 1 to 9
• a box containing graduated red rods from 1 to 9
• some paper
• a pencil

Example of a practical exercise:

1. FIRST STEP

1. Fetch the material and sit down at a table with the child
2. Show the child the chart, telling him it is the one for doing subtraction
3. Take the box of beige rods and ask the child to arrange them next to the chart, from the longest at the top to the shortest, so that they are aligned on the left
4. Take out the blue rods and place them to the left of the chart, take out the red ones and place them to the right
5. Tell the child that the result will always be read in the blue numbers, the numbers from 1 to 9
6. Start with 18-9: place the blue rod of 9 on the chart at the far right under the number 18 and ask the child to read the result
7. Write on the paper 18-9=9
8. Put the rod of 9 back, turned over to show that it has been used
9. Then take the rod of eight and place it starting from 18
10. Ask the child to read the result: 10. Ask whether we keep this combination (no, the result is a red number). Stop with 18.
11. Take 17: cover the number 18 with the beech rod of one. Take the blue rod of 9, place it starting from 17 and read 17-9=. Have the child write the combination on the paper, then ask him to read the result on the chart: 8. Invite him to write the result, then continue with the next subtraction 17-8
12. Then move on to 16: cover 17 and 18 with the beech rod of two and place the blue rod starting from 16
13. Continue this way down to 1-1, each time covering the numbers on the chart that do not concern us and using a sheet of paper for each number.

2. SECOND STEP: building the tables

On another day, ask the child which table he would like to do. Start, for example, with the table of nine

1. Take the beech rod of nine to cover the numbers from 10 to 18
2. Take the blue rod of nine, place it on the chart and read 9-9=
3. Write the operation, then ask the child to read the result: 0. Then write 0 on the sheet. Next take the blue rod of eight, place it on the chart starting from nine and say aloud: 9-8=. The child writes the operation, reads the result, then writes it
4. Take the red rod of one and place it under the number 1 on the chart to mark the result
5. Move on to the blue rod of seven, then to that of six, of five, of four, etc., taking care each time to write the operation on the paper and to place the red rod for the result.
6. Then continue with the following tables
7. To check the result, use the control chart