Reading a ruler is an essential skill that children typically learn in elementary school. Students usually enjoy this because it's a very hands-on process and has obvious applications in the real world. After teaching students the basics of reading a ruler, you can let them loose in the classroom, measuring a variety of objects they find.
Using a blown-up version of a ruler projected on a screen so that all students can see it, demonstrate the correct way to use a ruler. For example, students should learn that you should always start the measurement at the "zero mark." If possible, show different types of rulers, so that students can see that in some cases, the zero mark is at the end of the ruler, but in other cases, there is a small space before the actual readings start. When starting at the zero spot, students simply look at the number on the ruler to find the measurement.
The Broken Ruler
A broken ruler -- or one where the edge has been worn down to make the measurement inaccurate -- can be difficult for students to understand because they can't simply look at the measurement on the ruler for the answer. Instead, they have to subtract the number from the starting point. For example, if the student aligns the object starting at the "1" mark, and the object reaches the "7" mark, the object is actually 6 units. Students can do this without subtracting by counting the units along the ruler. Professional Development for Busy Educators suggests that students count the spaces rather than marks to avoid the mistake of counting the starting point.
Once students understand the basics of how to read a ruler, you can give them objects to measure and a paper to record their answers. To make this easy, start with items that are in whole units. As students gain confidence with the ruler, they can measure objects that have half- or quarter-units. Another activity once students have practice measuring is to have them practice estimating by challenging them to find objects in the classroom that have specific measurements.
American children will need to learn the metric system, since it's the standard around the world, as well as the imperial system, which is used in the U.S. Once students understand how to use one or the other, it's fairly easy for them to switch to the other. However, for fun, you might want to have students measure using other types of "rulers," such as how many hands or how many shoes an object measures.
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