In this unit, students will apply their knowledge of place value to help them add and subtract larger quantities. Students will extend the skills introduced in Unit 11 by developing the ability to write equations and explain their reasoning for how they solved problems with twodigit numbers. Also in this unit, students will learn how to add/subtract multiples of 10 using representations and mentally find ten more and ten less than a given number. In order for students to try on new strategies involving equations and mental math, they need to have a strong base ten understanding and background experiences with concrete tasks.
Key Concepts:
 When adding twodigit numbers, we add tens with tens and ones with ones (sometimes composing a ten).
 We can find ten more or ten less without having to count.
 We can use our understanding of place value to add and subtract ten to/from multiples of ten.
Prior Knowledge Needed:
 Understand Place Value (Grade 1, Unit 8)
 Adding Multiples of 10 with representations (Grade 1, Unit 11)
 Mentally find 10 more without needing to countÂ (Grade 1, Unit 11)
Units on the Horizon:
 Adding and Subtracting within 100 (Grade 2, Unit 1)
 Understanding 3digit Numbers (Grade 2, Unit 6)
 Using Place Value to Add and Subtract 3digit Numbers (Grade 2, Unit 11)
Lessons

Lesson objective: Identify when composing a new ten is necessary when adding two numbers. Students bring prior knowledge of using place value from 1.NBT.B.2. This prior knowledge is extended to using place value to help them add as students solve equati...

Lesson objective: Identify equations that require composing a new ten. This lesson helps to build fluency with deciding when a new ten needs to be composed. Base ten blocks are used here because it supports students in seeing how ten individual cubes ar...

Lesson objective: Decompose the singledigit number to make a new group ten when adding. This lesson helps to build procedural fluency with using equations to compose a new ten. Ten frames are used here to help with the transition to equations because t...

Lesson objective: Add twodigit and onedigit numbers together using the strategy of composing a new ten when necessary. This lesson provides an opportunity for students to apply their knowledge and understanding of place value to add numbers in a real...

Lesson objective: Understand that you can find ten more or ten less than a value without having to count by ones. Students bring prior knowledge of place value from 1. NBT.B.2. This prior knowledge is extended to mentally adding/subtracting a group of t...

Lesson objective: Find 10 more and 10 less than a number by using a hundred chart This lesson helps to build procedural skill with using a hundred chart to add or subtract 10. A hundred chart is used here because it supports students in adding or taking...

Lesson objective: Apply an understanding of place value to explain how a number changes when ten is taken away. This lesson provides an opportunity for students to apply their knowledge and understanding of place value to a mathematical situation. Stude...

Lesson objective: Understand that they can subtract groups of ten Students bring prior knowledge that it is more efficient to add by a group of ten instead of ten ones from Grade 1, Unit 11 (1.NBT.C.4). This prior knowledge is extended to include subtra...

Lesson objective: Solve subtraction problems with multiples of ten by using a strategy. This lesson helps to build fluency with subtraction problems using multiples of ten. Base ten blocks and an open number line are used here because they support stude...

Lesson objective: Apply place value subtraction strategies to solve problems using multiples of ten. This lesson provides an opportunity for students to apply their knowledge and understanding of place value subtraction strategies a mathematical situati...