This is a culminating unit in which students demonstrate fluency and are expected to use and explain strategies for accurate and efficient addition and subtraction. By this time in the year, students should be able to solve all problem types in Table 1 in the Common Core State Standards for Mathematics using concrete models or drawings and strategies for addition and subtraction to 1000.
Key Concepts:
 Understanding the place value system allows us to fluently add and subtract numbers within 100.
 We can use addition and subtraction in many different ways.
 The strategy we use to add or subtract does not change the total or difference.
 Knowing some addition and subtraction facts from memory helps us solve new addition and subtraction problems.
Prior Knowledge Needed:
 Developing strategies for addition and subtraction (Grade 1, Unit 6)
 Extending strategies for solving addition and subtraction problems (Grade 1, Unit 9)
 Adding and Subtracting Within 100 (Grade 2, Unit 1; 2.OA.B.6)
Units on the Horizon:
 Exploring equal groups as a foundation for multiplication and division. (Grade 3, Unit 1)
 Developing strategies for addition and subtraction (Grade 3, Unit 3)
 Investigating patterns in number and operations (Grade 3, Unit 8)
 Developing strategies for multiplication and division (Grade 3, Unit 9)
Lessons

Lesson objective: Understanding that place value can help us add and subtract numbers more fluently. Students bring prior knowledge of place value from 2.NBT.1. This prior knowledge is extended to include how thinking about the number of tens and one in...

Lesson objective: Fluently solve addition and subtraction problems using an understanding of place value. This lesson helps to build fluency with number decomposition. Decomposing numbers is used here because makes the numbers in the problem easier to w...

Lesson objective: Apply an understanding of how to decompose numbers to help solve addition and subtraction problems. This lesson provides an opportunity for students to apply their knowledge and understanding of using the place value system to add and ...

Lesson objective: Extend understanding that addition and subtraction can be used in different ways. Students bring prior knowledge of addition and subtraction from 2.OA.1. This prior knowledge is extended to include an understanding of more ways additio...

Lesson objective: Fluently add and subtract numbers in different ways using a number line. This lesson helps to build fluency with adding and subtracting numbers within 100. A number line is used here because it clearly shows how students are thinking a...

Lesson objective: Solve a riddle using addition and subtraction strategies. This lesson provides an opportunity for students to apply their knowledge and understanding of adding and subtracting twodigit numbers to a mathematical situation. Students are...

Lesson objective: Understand that creating an equivalent expression can be used as a strategy to solve a subtraction problem. Students bring prior knowledge of addition and subtraction from 2.OA.A.1. This prior knowledge is extended to get comfortable w...

Lesson objective: Use equations as a strategy to fluently add and subtract. This lesson helps to build fluency with addition and subtraction. Equations are used here because they supports students' comprehension of the word problem. This work develops s...

Lesson objective: Apply addition and subtraction skills to create word problems. This lesson provides an opportunity for students to apply their knowledge and understanding of adding and subtraction twodigit numbers to a mathematical situation. Student...

Lesson objective: Solve addition and subtraction problems mentally. This lesson provides an opportunity for students to apply their knowledge and understanding of addition and subtraction strategies to a realworld situation. Students are asked to menta...

Lesson objective: Fluently add and subtract within 20 using mental strategies. Students bring prior knowledge of using place value understanding and properties of operations to add and subtract from 2.NBT.B. This prior knowledge is extended to include m...

Lesson objective: Fluently subtract a given number from 13. This lesson helps to build fluency with mental calculations. Mental strategies are used here because it helps students understand that problems can often be worked out in several different ways...

Lesson objective: Fluently add and subtract within 20 using mental strategies. This lesson helps to build fluency with adding/subtracting within 20 using mental strategies. The game "Closest to 20" is used here because it requires students to think abou...

Lesson objective: Fluently add and subtract within 20 using mental strategies. This lesson helps to build fluency with adding/subtracting within 20 using mental strategies. The game "What's My Number?" is used here because it requires students to both a...

Lesson objective: Apply strategies to mentally create number combinations within 20. This lesson provides an opportunity for students to apply their knowledge and understanding of mental math strategies to a mathematical situation. Students are asked to...