# Gr. 1 Unit: Add & and Subtract within 20

**LESSON UNIT**

- ADD AND SUBTRACT WITHIN 20 (DOCX)

**LESSON PLANS**

**LESSON SEEDS**

- COUNTING BY 2’S TO ADD OR SUBTRACT (DOCX)
- BUILDING MODELS (DOCX)

### UNIT OVERVIEW

In Grade 1, students extend their prior work with small numbers to begin developing strategies for adding and subtracting whole numbers using a variety of models. These models include discrete objects to model add-to, take-from, put-together, take-apart, and compare situations to develop meaning for the operations of addition and subtraction. These models also help to develop strategies to solve arithmetic problems which involve these operations. Students understand connections between counting and addition and subtraction (e.g., adding two is the same as counting on two). They use properties of addition to add whole numbers and to invent and use increasingly sophisticated strategies based on these properties (e.g., “making tens”) to solve addition and subtraction problems within 20. By developing, discussing, and comparing a variety of solution strategies, children build their understanding of the relationship between addition and subtraction.

**Essential Questions:**

- Why do I need mathematical operations?
- How do I know which mathematical operation to use?
- What are different ways to count?
- What are the most efficient ways to count?
- In what ways can numbers be composed and decomposed?
- What questions can be answered using addition and/or subtraction?

A question is essential when it stimulates multi-layered inquiry, provokes deep thought and lively discussion, requires students to consider alternatives and justify their reasoning, encourges re-thinking of big ideas, makes meaningful connections with prior learning, and provides students with opportunities to apply problem-solving skills to authentic situations.

**UNIT LESSON:**

Additional information such as Teachers Notes, Enduring Understandings,Content Emphasis by Cluster, Focus Standards, Possible Student Outcomes, Essential Skills and Knowledge Statements and Clarifications, and Interdisciplinary Connections can be found in this Lesson Unit.

**AVAILABLE MODEL LESSON PLANS**

The lesson plan(s) have been written with specific standards in mind. Each model lesson plan is only a MODEL - one way the lesson could be developed. We have NOT included any references to the timing associated with delivering this model. Each teacher will need to make decisions related ot the timing of the lesson plan based on the learning needs of students in the class. The model lesson plans are designed to generate evidence of student understanding.

This chart indicates one or more lesson plans which have been developed for this unit. Lesson plans are being written and posted on the Curriculum Management System as they are completed. Please check back periodically for additional postings.

Finding Unknown Addend Combinations

CCSC Alignment: 1.OA.C.6

Students identify multiple combinations of two addends that result in a sum of 20 when solving a word problem, identify strategies used to solve addition facts, and justify why the chosen strategy is the most efficient.

**AVAILABLE MODEL LESSON SEEDS**

The lesson seed(s) have been written with specific standards in mind. These suggested activity/activities are not intended to be prescriptive, exhaustive, or sequential; they simply demonstrate how specific content can be used to help students learn the skills described in the standards. Seeds are designed to give teachers ideas for developing their own activities in order to generate evidence of student understanding.

This chart indicates one or more lesson seeds which have been developed for this unit. Lesson seeds are being written and posted on the Curriculum Management System as they are completed. Please check back periodically for additional postings.

Counting by 2’s to Add or Subtract

CCSC Alignnment: 1.OA.C.5

Students use their understanding of counting by 2’s to become proficient in adding or subtracting by 2.

CCSC Alignnment: 1.OA.C.6

Students take equations such as 8 + 4 = ? and change them to make easier combinations using their mental math strategies. For example, changing the equation to 8 + 2 + 2 = ? students know that 8 + 2 = 10 and so 2 more is 12.