## Reflection: Intervention and Extension Mentally Speaking! - Section 2: Applying the Knowledge!

While students were working, I noticed they did not all recognize they were using the same strategies that they used for single-digit numbers,  such as counting on, counting back, and looking for tens. These strategies can be applied to greater numbers as well.

To brighten their awareness, I divide students up into smaller groups. I give each group base ten blocks, place value charts, and number lines. First we work on adding and subtracting one-digit numbers. I point out that when working with one-digit numbers, the digits are in the ones place. I write 7, 6, and 9 on the board. I ask students to represent each number using their materials. I want to make sure they fully understood, so I ask them to insert the numbers one-by-one in their place value chart. They do very well. Then I write 34 on the board. I ask what number is in the ones/tens place. After that, I write 33 on the board. I ask students how to correctly align these numbers in order to add them.

34 + 33 =

They explain which digits are in the ones and tens places. I point out that when using the algorithm, we can use single-digit addition strategies to add the digits within each place. For instance, 4 and 3 are in the ones place. So, 4 + 3 = 7. Similarly, 3 and 3 are in the tens place. So, 3 + 3 = 6. That means 34 + 33 = 67.

I repeat this a couple more times, or until students are able to see the pattern on their own.

What I noticed!
Intervention and Extension: What I noticed!

# Mentally Speaking!

Unit 1: Numbers & Operation in Base Ten Grade 2
Lesson 5 of 10

## Big Idea: Using base ten blocks and place value, students explore how to become more fluent in adding and subtracting two-digit numbers without regrouping.

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35 teachers like this lesson
Standards:
Subject(s):
Math, Place Value, Number Sense and Operations, reasoning, discussions, base ten, Mental Math
40 minutes

### Carol Redfield

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