## Lesson: Addition and Subtraction Facts to 20

Developing the Concept

Once children are comfortable with using a few different strategies to solve addition and subtraction problems, encourage children to apply them to the facts to 20. If manipulatives such as cubes are available, children may find it helpful to use them and fact cards. You will use many of the same strategies that you used in facts to 10 and add several new ones. Encourage children to share the strategies they use and tell why they used them.

**Materials:** snap cubes or other available items, such as paper clips, fact cards, pencils, paper

**Preparation:** Prepare fact cards for addition facts through 20 and for the corresponding subtraction facts. Write the strategy on each card.

**Prerequisite Skills and Concepts:** Children should have a good foundation in addition and subtraction facts through 10.

**Wrap-Up and Assessment Hints**

Find out which facts children have mastered and which facts they need help with. If a fact has not been mastered, ask children how they might go about figuring it out. Find out what they are thinking and then select a strategy that builds on what they already know. Encourage children to use number relationships and fact families.