## Addition and Subtraction Facts To 20

Begin by focusing on addition facts through 10. When children have become proficient in these, introduce the corresponding subtraction facts. Put the facts in the context of a story. Act them out and encourage children to follow along with their cubes. Once children are comfortable with all the facts, encourage them to use the fact cards for practice.

Materials: snap cubes, fact cards

Preparation: Prepare fact cards for addition facts through 10 and for the corresponding subtraction facts. Write the strategy on each card. Hand out 10 cubes to each child.

Prerequisite Skills and Concepts: Children should have a good foundation in number relationships.

• Say: We are going to learn a new skill called addition. I need some volunteers to help me act out a story.
Choose 3 children to come to the front of the class. Have the class count the 3 children. Then ask 1 more child to come to the front of the room and count again.
• Ask: What did we do?
Children should say that 1 more child joined the group, or 1 more child was added to the group.
Explain that 1 child was just added to the group. Write the addition sentence on the chalkboard. (3 + 1 = 4)
• Say: Let's try it again. You can act out the problem with your cubes.
Continue as above, using numbers to 9 with 1 child joining the group.
• Ask: Do you see a pattern here?
Children should see that the number went up by 1 each time.
• Say: Now we are going to try something different.
Repeat the activity, only this time call different numbers of children, but don't add more children to each group.
• Ask: What did you notice this time?
Children should notice that if no children are added to the group, the number remains the same. (e.g., 3 + 0 = 3, 5 + 0 = 5)
• Say: I would like you to put 2 cubes of 1 color together. Now put 1 cube of another color on your cube train.
• Ask: What does this show you?
That there are 2 cubes and 1 cube, 2 and 1 more is three.
Write 2 + 1 = 3 on the chalkboard.
• Say: Now flip your cube train end to end and tell me what you see.
That there is 1 cube and 2 more cubes, 1 and 2 more is three. Write 1 + 2 = 3 on the chalkboard.
• Ask: What did we do that was the same? What did we do that was different?
Make sure children recognize that the order of the addends didn't change the sum. Repeat with some other facts.
• Say: If you know an addition fact, you can put it in a different order and you will know another fact. So, if you know 1 fact, you know 2 facts.
• Say: Use your cubes. Put 5 cubes together. Now add 1 more cube.
5 + 1 = 6. Write it on the chalkboard.
• Ask: How can we undo what we just did?
Take away 1 cube.
• Ask: What number sentence shows what we just did? 6 – 1 = 5.
Write the sentence on the chalkboard. Tell children that these two facts are related. If they know an addition fact, they know a subtraction fact too!
• Ask: What other addition fact can you make with 5 + 1 = 6?
Elicit 1 + 5 = 6. Write it next to 5 + 1 = 6.
• Ask: Do you think you can make another subtraction fact with 6, 1, and 5?
Children should say that they can make 6 – 5 = 1.
• Say: These four facts make a fact family. If you know one of these facts, you can figure out all the others in the family! Now, can we make a fact family with 3, 5, and 8?
Help students write the four sentences in the family.
• Ask: Now, let's try another one. Make a cube train of 3 cubes. Now add 3 cubes of another color. What fact can you write?
The fact is 3 + 3 = 6.
• Ask: What happens if you remove 3 cubes from the 6 cubes you now have? What is the fact?
Children should say that they have 3 cubes remaining. 6 – 3 = 3
• Ask: Can you write any more facts for this family?
Encourage children to see that doubles such as 3 + 3 have only two members to their family.