Subtraction Strip Board
Materials:
The Subtraction Strip Board (This board is read right to left, so the vertical blue line is after the ten- serving the same purpose as the red line on the Addition Strip Board).
Blue strips 1 - 9
Red strips with partitions 1 - 9
17 unmarked wooden strips
Prepared subtraction tables
Pencil, Pencil holder
Squared paper
Subtraction Chart I (Control Chart)
Large Table (or 2 individual tables)
Purposes: To memorize of the essential subtraction combinations
Age: 5 - 6
Preparation:
The child has had the first presentation with the Subtraction Snake Game.
The child has done Subtraction on the Stamp Game
Presentation 1: Building the Essential Combinations
Invite the child to the lesson, decide who brings the board, strips, and writing tray.
Introduce the board, numbers 1-18, the blue line, and the familiar strips.
Invite the child to set up the blue strips as before on the top left side of the table
Introduce the wood strips and remove them from the box.
Arrange the wood strips from longest to shortest on the right side of the board. Set a few and transfer to the child
Explain you will do subtraction. The blue strips represent how much you will take away.
Child writes their name on the book.
Show child first problem in the book and read it with them: 18-9=
Point to the 18 on the top of the board.
Take the blue nine strip and set it on top of the numbers right edge covering the 18.
Indicate to the first number before the strip is the answer.
Child writes the answer and then replaces the blue strip
Explain that we only write the answers that show up in blue (you can place a smaller blue strip to show how the answer will be red.)
Turn the page 17-9=
Child reads the equation
Model how to make the board read 17 by placing the smallest wooden strip on the 18 so the last number on the board is 17.
Have the child repeat with the blue strip and record the answer.
Continue for the table of 17, remove wood strip when done
For the next table of 16. Select the next wood strip up and place it on the number so that the 16 is the last number showing.
When the child is ready, show them the control Chart I
Have the child read the first equation in her book and find it on the chart. Read both to verify
Presentation 2: How Many Ways
Set up the strips and board as in presentation 1 with the addition of the red strips below the blue. The child will need a book with grid paper.
Explain you will find out how many ways to make a number-Example: 7
Find the correct wooden strip, counting down the stair to 7, and place the strip over the numbers so the 7 shows.
Place a blue 1 on the right side under the 7 on the board.
Ask how many more are needed to make 7.
Have the child count the spaces to the left. Place the red 6 to the left of the blue 1
Have the child place the blue 2 under the combination, count the spaces to make 7, and place the red 5.
Continue until all combinations are found
Give the child a booklet to record the combinations
Tell the child the blue strips represent what we are taking away
Point to the 7 and say, “7 minus 1” pull down the blue 1 to the lower right, “equals 6.” pull down the red 6 to the lower-left portion of the board.
Child records
Replace the strips to the side of the board
Allow the child to continue.
The child will check their work with Chart I.
Control of Error: The subtraction control chart
Pedagogical Notes:
The child could verbally repeat each math fact four to five times throughout their work with the strip boards!
First, they read the equation in the booklet
They say it as they place the strips
They say it as they are writing it down
They will read it on the control chart as they check it in the booklet
Encourage the children to check their work because the result matters and it encourages repetition.
The book only offers an equation that will have a blue answer.
The number colors are reversed to show that what we are doing is opposite and to distinguish the two boards
For example, 18-6=12 (a red answer) is not considered an essential combination. The child will need to memorize 8-6=2. The child will only memorize the facts that allow them to work within a single category.
