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Subtraction Snake Game

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5. Subtraction Snake Game

Material

A collection of colored bead bars, boxed (minimum of 5 colored bead stairs).
Golden 10 bars, boxed (minimum of 20).
One black and white bead stair, boxed.
Gray negative bead stairs, boxed (minimum of 3 sets).
A notched card for the “bridge.”
A felt underlay – standard black or color-coded green.
All items fit on a tray.

Presentation

1. Invite the child to the lesson.
2. Show him the subtraction snake game.
3. Ask him to bring the material on a tray, to a table.
4. Show the child the grey beads.
5. Point out the similarities of the grey beads to the black and white beads; look at the light and dark shades of the grey beads.
6. “These beads are going to be used for taking away. What are we going to use them for? Right, take away. I bet you want to see what I mean!”
7. Put grey beads back in the box.
8. Ask the child to build the black and white bead stair.
9. Ask the child to build a snake with the colored bead bars.
10. As the child places colored bead bars, place grey beads in the snake.
11. Ask the child to count the beads and turn the snake gold, just as before.
12. Once the child reaches a grey bead bar, ask the child to stop counting.
13. “Oh, here are grey beads! We are going to have to take them away! How much do we need to take away?” For example, “Right, five!”
14. Count back that many beads.
15. Look to see how many beads are left over on that bar.
16. Place black and white beads above the bar as a placeholder.
17. Slide the bead bar and the grey bead bar down on the underlay.
18. Place the bars back in their boxes just as you did with the addition snake game.
19. Place the grey bead bar in the same box with the colored bead bars that made the snake but were exchanged for golden bars.
20. Close the snake, connecting the colored beads to the black and white beads.
21. Continue counting the snake, turning it gold.
22. Repeat the same process as above when you encounter another grey bead bar.
23. Once the child is done, admire the snake and emphasize how much shorter it is.
24. Place the beads back in their proper boxes and clean up.
Proof
1. Invite the child to the lesson.
2. Ask him to build a snake, just like he did in the presentation.
3. As the child builds the snake, add grey beads just as before.
4. Repeat the same process, but this time when the child finishes everything, show him how to use the proof.
5. “It sure would be cool if we could check to see if the snake is just the right number. I can show you how to do this!”
6. Place a couple golden 10 bars vertically on the left side of the underlay.
7. Ask the child to place the rest of the golden bars.
8. Place the grey bead bars with the golden ones.
9. Place the colored bead bars vertically, on the right side of the underlay.
10. Repeat the same process as was done for the first proof of the addition snake game.
1. Invite the child to the lesson.
3. When the child reaches a grey bead bar, ask him to stop.
4. Isolate the grey bead bar by disconnecting it from the snake and placing it above the bar(s) that you will be taking away from.
5. Count backwards that amount of beads, just as before.
6. Look to see how many beads are left over on that bar.
7. Place black and white beads above the bar as a placeholder.
8. Slide the colored beads that were taken away from, and the grey bead bar, down.
9. Close the snake.
10. Place the beads that were taken away from and the grey bead bar in the container as before.
11. Hand off to the child again and make sure the child continues this process when he has to take away beads again.

Exercises

Child works independently.

Direct Purpose

To gain familiarity with the subtraction combinations.

Indirect Purpose

Indirect preparation for algebra.

The proof.

5 1/2 to 6

Notes

Very important to stay with the beads; Maria Montessori noticed that taking away beads for subtraction work diminishes the child’s interest.