Prepare for the activity by selecting some items in the class that you will ask the students to measure. The items should have a wide range of heights, from a few inches to several feet. Label each item with its name. To make the activity more applicable to everyday life, leave the items in their usual spaces but make sure the labels are easy to see. You should label at least one item in the class for each pair of students -- for example, at least 15 items for 30 students. Measure and record the height of each item as accurately as possible.
Set up two tables, one with measuring tapes and another with rulers. Instruct students to get into groups of two and select either a tape measure or a ruler. Tell students that they will eventually use both so there is no rush to go to one table or the other.
Instruct students to measure the height of five different labeled items. They should record the name and measurement of each item on a piece of paper.
Instruct students to switch measuring tools, from ruler to tape measure or tape measure to ruler. Ask them to measure and record the height of five more objects, which should not be the same as the previous five.
Tell students to return to their desks and hand out a sheet that lists all the measurements for the different items that you found before the activity began. Ask students which measuring tools were the most accurate. Was one tool always more accurate then the other? Most students will find that the tape measure was more accurate for taller objects, but there was little difference with shorter ones. Ask students which tool was easier to use on which objects and why they think it was easier. In this case, many students should have found the ruler easier to use on smaller objects.
Give students a sheet with a list of various items of different lengths and tell them to write down which kind of measurement tool would work best on each item. After students are done, ask them how they would measure something such as the length of a blue whale or a single hair, which could not easily be done with either tool.