Begin by helping your child cut out different shapes from paper.
Use an inch or centimeter ruler to draw and mark off the sides of
squares, rectangles, triangles, and other shapes in whole units (such
as 5 centimeters or 3 inches). After cutting out a square or rectangle,
ask your child to find the area it covers in square units (square
inches or square centimeters).
If your child knows the formulas, he should use them. Then ask
him to explain why these formulas work. If he doesn’t know
the formulas, encourage him to draw square units with a ruler on the
shape (by marking off units on the edges and then drawing lines straight
across). Then he can count the squares. Ask him to find the areas
of other rectangles and squares and try to come up with a quicker
way of doing it (without drawing and counting). In this way, he can
find the formulas on his own.
For example, if your child is exploring a rectangle that is 5 inches
long and 3 inches wide, he can use a ruler to draw square units on
the shape. He can then count up all the squares to get an area of
15 square units. He will remember that 3 times 5 equals 15. He will
also see from his shape that he has 3 rows of 5 squares, which is
a way to model 3 times 5. After doing this a number of times, he will
begin to understand that the way to find the area of a rectangle (or
a square) is to multiply length times width.
Once your child has determined a quick way to find the areas of
squares and rectangles, try triangles next. Again, help him see how
formulas relate to drawing and counting squares and produce the same
results. Help him understand why the formulas
work. Don’t worry if you don’t know or remember all
the formulas. After working with your child on this activity, you
will.
Next, you and your child can work on finding the area of other,
more complicated shapes such as those in this picture. Encourage your
child to make connections between finding the areas of these new shapes
and finding the areas of such basic shapes as squares, rectangles,
and triangles.
