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Measurement of Length

Children's thinking about measuring length is the topic of this newsletter. Measurement problems, like arithmetic problems, are basic to daily experience and arise in many different situations. It is important for children to have opportunities to learn more about measurement. They learn through thinking about measurement problems. Knowing about how children tend to think about measurement helps adults to guide children's discovery of the principles of measurement.


Principles about Measuring

If children are simply told to measure length in a unit like an inch, they develop very little understanding of the principles of measurement. Children need the opportunity to understand principles about measurement. These principles include:

1. Appropriate units
Use units of measure appropriate to the thing being measured. Units that work for measuring the length of your driveway may not work for measuring the length of your notebook. Units used to measure length may not serve well for the measurement of area.

2. Identical units
To say that a candy bar is 5 inches long means that every inch is exactly the same.

3. Measurement conventions
Standard units like inches exist as the result of discussions and agreements among people about measurement problems. The "foot" we use today comes from the length of a certain king's foot. People in his kingdom adopted this as a standard that has been passed on. When children participate in the process of forming conventions, they come to see their utility.

4. Iteration
Measurement means repeated application of identical units.

Paper Clips

Children's Thinking about Length

Primary grade children usually have some knowledge of units of measurement. They often know that smaller units (like inches) will result in a larger number to describe an object's length than larger units (like feet). Children can use unconventional items like paper clips to measure lengths. Using such materials to solve measurement problems requires that children consider the meaning of a measurement unit. Asking children to solve problems about the measurement of length emphasizes inventive thinking rather than rote use of rulers.

Children need to learn that identical units must be used when measuring. They usually need experiences working on and discussing measurement problems to understand why identical units are necessary. We have observed teams of children happily mixing adult and child shoes of different sizes to measure the length of a classroom. They then confidently reported that the room was a certain number of shoe lengths long. Following this experience the teacher asked the children to explain why each team got a different "length" of the same room. Only then did it occur to the children that they had not used identical units. Through this discovery children came to realize the importance of identical units for accurate measurement.

Most children understand the idea of iteration. However, they may have trouble simultaneously keeping track of the number of times they have repeated the measure and the place they have left off. Making marks may help children keep track of their place.

Parents Corner