Show the kids a variety of rulers such as plastic, wood and metal. Allow the kids to look at the numbers on the ruler. Explain to them the reason why a ruler is used. Tell them that 1 foot is equal to 12 inches. Teach them about the abbreviations that are used in measurement such as inch (in.) and foot (ft).
Explain to the children the history of inches and how the width of thumb was used to measure in ancient times. Let the children draw a line that is equal to the width of their thumb on a piece of construction paper. Let at least 12 children measure their thumb and cut the paper, then use the ruler to determine the actual measurement.
Demonstrate to the children how to line up the first line on the ruler with the left-hand edge of the object. Explain to them that when they are measuring, where the object ends is the measurement.
Let the children practice to read a ruler for third grade math by doing various activities. These activities should involve measuring, such as doing wood work, sewing or building models.