## 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

Unit 8: Numbers Have Patterns
Lesson 11 of 14

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

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Standards:
Subject(s):
Math, Number Sense and Operations, Algebra, Patterns (Algebra), Place Value, subtraction, addition, place value strategies
70 minutes

### Beth McKenna

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