that in this lesson, the balance model for subtraction will be
demonstrated using both an actual and a virtual pan balance.
Display a pan balance and review with the students how it
operates. Explain that when the scale balances, both sides have the
Then ask a volunteer to place 7 connecting cubes in the left pan
of the balance beam and 4 connecting cubes on the other side. Ask the
students how many connecting cubes are needed on the lighter side so
that the scale balances. Accept and model all student responses. When
the response “3” is given, ask the children what question “3” answers.
[How many more than 4 is 7?] Then ask them to record the answer using
the equation form 7 – 4 = 3. Ask if they know what addition sentence
would also fit the situation. [3 + 4 = 7 or 4 + 3 = 7.] Continue with
other weights until the students are comfortable with the process.
Divide the students into pairs and give each pair a die.
Assign each child one side of the pan balance. Tell individuals to roll
the die, read the number of dots on the upward face, and place that
number of connecting cubes on their side of the balance. Then have
partners work together to balance the scale by adding connecting cubes
in a different color. They should record the subtraction equation that
shows what they did. Have them repeat the activity several times.
Now call the class together and demonstrate how to use the Pan Balance - Shapes tool.
Assign some students to work with this site. Because the shapes
represent different values, advise the students to use only one shape
as they explore with the online balance. While some children are using
the online balance, others can play “What’s in the Bag?” To start the
game, provide pairs of children with a pan balance, a paper bag, and
some connecting cubes. Assign one child to go first, placing up to 10
connecting cubes in the bag and placing the bag on the left side of the
scale. Then that child will place up to 10 loose connecting cubes on
the right side. The other child is to add connecting cubes to the
lighter side until the scale balances. Then each child writes
subtraction and addition equations to describe the situation. Have them
repeat the activity several times, switching roles each time.