##
* *Reflection: Checks for Understanding
Let's Review - Section 1: Let's Review Adding More Than 2 Numbers

As I watch students working to add 3 and 4 2-digit numbers, I often find half understandings and misconceptions. I notice that when they add the tens and ones in a problem (such as 15 + 26 + 14 + 35=), they begin by adding 5 + 5 and 6 + 4 to get 10 + 10 = 20. But then they add 1 + 2 + 1 + 3 and get 7, so they add 10 + 7 and get 17 for an answer. They do not look back at the original numbers to see that 17 cannot possibly be the number. They are adding the tens and then adding the ones. The piece that they are still confused about is that the 7 represents 7 tens or 70.

This is a half understanding, where they know that tens and ones are separate, but by the end of the problem, they have forgotten that the 7 represents 7 tens so they add it in as ones.

My job here is to reinforce what the digit in the tens place represents. I can do this with base ten blocks, with drawings, and also by having the children count the tens on the number line so they would add 10 + 20 + 10 + 30 and see that they have landed at 70.

Students at this age need the visual representation of the value of tens and ones to help clear up the misconception/half understanding that they are working with as they try to solve problems.

*Misconceptions and Half Understandings*

*Checks for Understanding: Misconceptions and Half Understandings*

# Let's Review

Lesson 11 of 14

## Objective: SWBAT explain the strategies they are using to complete addition and subtraction problems with 2-digit numbers.

## Big Idea: Revisit, Revisit, Revisit! Students need repeated exposure to math concepts to really understand how they work.

*70 minutes*

I tell students that today we will go over some of the things we have been working on for the past few weeks. I begin by writing the following on the board:

15 + 23 + 25 + 27 =

I ask students to think of what might help with solving this problem (model with math MP4) (partners of 10, adding tens, adding ones, using a number line or number grid.) I ask them to choose a strategy and solve the problem.

I give students a few minutes to work and then ask for a volunteer to come up and show us how they solved the problem. I ask if anyone solved it differently and if they can show us what they did. We discuss the similarities and differences in the approaches.

I now put up a second problem:

15 + 35 + 32 + 38

I ask students to think about what they just saw their classmates doing as they made sense of the problem and solved it (MP1), and what they did, and to solve this problem. Again we share several different solutions.

I tell students that today we will be working in centers and I ask them to clear their desks and be ready to listen to the directions for each center. I count back from 35 to give students time to clean up.

*expand content*

#### Centers

*45 min*

I explain the 3 centers to the students and tell them that they will rotate through all 3.

Center 1: At this center students will be working on ways to create and solve 2-digit subtraction problems using manipulatives for support (make sense of problems and solve them MP1). Students will review subtraction houses and how to build a larger number and take away from that number to find an answer. The written problem will be posted to allow students to see how the problem looks on paper as well as how it is solved concretely.

Center 2: Students will use their base 10 blocks to arrange 4 digits into different subtraction problems to determine the greatest and least possible answers (model with mathematics MP4). Example, I give the students the digits 4, 5, 6, 7. The possible subtraction problems are 76 - 45, 76 - 54, 75 - 64, 75 - 46, 74 - 65, 74 - 56, 67 - 45, 67 - 54, 56 - 47. Students can solve these to find the greatest and least possible answers.

Center 3: Students will write a subtraction number story for others to solve. They will draw 4 cards to create 2 2 digit numbers. They will then use those numbers to write a number story. They will solve the story and write the answer on the back. They will exchange stories and solve each other's stories.

*expand content*

#### Closing

*10 min*

I bring students to the rug to close today's lesson. I have gathered up the word problems that they wrote. I invite several students to come up to the easel to solve the problem of a classmate. I invite a child to read his/her problem while 2 children work at the easel to solve it. The rest of the group can try to solve the problem in their heads, or watch what the 2 children are doing. If the child at the easel becomes stuck, they can ask for help from a classmate.

*expand content*

Susan, I am so glad that you found the houses helpful. My students have always enjoyed them and seem to grasp the new concepts by using them. I hope your students have fun with them.

| 2 years ago | Reply

AMAZING! I love the subtraction houses!!! THANK YOU for the great center ideas too!

| 2 years ago | Reply##### Similar Lessons

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- UNIT 1: What and Where is Math?
- UNIT 2: Adding and Subtracting the Basics
- UNIT 3: Sensible Numbers
- UNIT 4: Sensible Numbers
- UNIT 5: Everything In Its Place
- UNIT 6: Everything in Its Place
- UNIT 7: Place Value
- UNIT 8: Numbers Have Patterns
- UNIT 9: Fractions
- UNIT 10: Money
- UNIT 11: The Numbers Are Getting Bigger
- UNIT 12: More Complex Numbers and Operations
- UNIT 13: Area, Perimeter and More Measurement
- UNIT 14: Length
- UNIT 15: Geometry
- UNIT 16: Getting Ready to Multiply
- UNIT 17: Getting Better at Addition and Subtraction
- UNIT 18: Strategies That Work

- LESSON 1: Using A Pattern to Solve A Problem
- LESSON 2: Skip Counting Patterns
- LESSON 3: Extending Partners of 10 and 100
- LESSON 4: Patterns in Larger Numbers
- LESSON 5: Larger Numbers: A Tie to Social Studies
- LESSON 6: Doubles and Halves are Patterns Too
- LESSON 7: Smiley Faces and Up
- LESSON 8: Put It Together and Take It Apart
- LESSON 9: Pets, Pets and More Pets
- LESSON 10: Larger Number Patterns
- LESSON 11: Let's Review
- LESSON 12: Patterns in Nature
- LESSON 13: Writing and Solving Number Stories
- LESSON 14: Trimester Assessment Day