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Unit: 1.4

Adding and Subtracting within 20

In this unit students

•  solve problems in all adding and subtracting contexts within 20;
•  make adding and subtracting strategies within 20 explicit.

Once students have a solid understanding of 10 as a bundle of 10 ones, they focus on addition and subtraction within 20. In this unit they solve problems in all adding and subtracting contexts within 20 and work to make their strategies for adding and subtracting explicit. One key strategy, making a ten, plays a prominent role in this work, as does the number line.

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Kathleen says:

3 months

I wonder about using ten frames for composing and decomposing ten and double ten frames for composing and decomposing 20? In what way is a number line the best choice at this stage? My experience shows that with children thinking literally, when . you introduce the number line, even after experiences with measurement (described previously), they understand the numbers on the line to represent those points only. To understand "7" on a number line as "including the distance before 7" is an abstract meaning for them. Another tool in addition to the ten frames that I have used with success is place value mats. Actually, ALL of Kathy Richardson's activities in her 3-volume set "Developing Number Concepts" have real practical value, particularly the ones in Volumes 2 and 3 which relate to addition and subtraction within 10, within 20 and place value. She doesn't use a number line and I wonder why. What has your experience been with introducing a number line in first grade?