### Measurement

During this time, many of the cognitive structures of measurement are still developing. Two of the most important of these are transitivity and conservation of length. An understanding of transitivity allows children to compare two lengths even if they are not right next to each other. For example, if shown two towers that are not next to each other and asked if he can use a dowel rod to compare their heights, a child with transitive thought can compare the first tower to the rod and then use the rod to assess the height of tower two, to determine if they are the same. Conservation of length is the understanding that length remains constant regardless of appearance. These two concepts should be the focus of the kindergarten measurement program. In this way, kindergarten children can begin to develop an understanding of iterated units of measurement, such as a ruler broken down into inches (Clements & Stephan, 2004). Iterated units of measurement can be either standard, such as inches or meters or nonstandard, like shoes or paperclips. Both can be used the same way in unit iteration, but a standard unit makes it more efficient for a society to communicate measurements. Some research has shown that the coordination of these two cognitive developments can take until fourth grade to develop to a point where children can use measurement techniques efficiently and flexibly. However, activities and interactions using nonstandard units to find the length of classroom objects support the early development and coordination of these concepts. For example, kindergarteners can use paperclips to measure the length of their books or desks. Children also begin to understand the measurement of area and can cover a picture with a number of squares and then count the squares. They can compare the number of squares it takes to cover different shapes, objects, and pictures.

### Units of Time.

Kindergarten children begin to understand that time can be divided into units such as hours, minutes, and seconds. However, it is often hard for them to mentally gauge the passage of time using these units. For example, a child may be told that the class will be going to the playground in 15 minutes. Five minutes later the child may ask, “Has it been 15 minutes yet?” With kindergarteners, it is often a good idea to use clocks to help them gauge time. The teacher can then say, “It will be 15 minutes when the big hand is on the 12.” Time is most relevant to the kindergarten child when it is linked to his daily schedule and everyday activity. It is difficult for him to link the understanding that time can be segmented into units with how long those units are, because the passage of time is based on perception. The old adage “time flies when you are having fun” is true. Fifteen minutes sitting outside the doctor’s office waiting to get a shot feels a lot longer than 15 minutes playing on the playground.

### Patterns and Algebra

Children’s classification schemes are more complex than they were in preschool. Kindergarteners can now sort objects by one or more attributes. They also use mathematical attributes to sort and seriate objects or groups of objects such as, “This pile has eight this one has four, and this one has two.” They can also sort objects into three distinct classes, such as small, medium, and large. Kindergarten children are also becoming better at using their representational abilities to make mathematical models (Dolk, 2004). Katherine Fosnot describes mathematical modeling as part of “mathematizing,” or the process of using mathematics to structure the world rather than just “learning” it. In her book Young Mathematicians at Work (Fosnot & Dolk, 2001), she shows how children use mathematical models. In one example, a teacher showed children a picture biscuits on a worksheet and asked them if there were enough for everyone in the class to have one. Three students decided to use small cubes to model the problem letting the cubes stand in for biscuits. When asked what they were going to do with the cubes, one child began to put red cubes on each of the biscuits while another gave a brown cube to each child in the class. Once each biscuit had a red cube on it, she counted them and got 22. The other child finished handing out the brown cubes and after ensuring that everyone received one, began collecting the cubes and counted 15. The students then said there were enough, because “22 is more than 15.”

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