SWBAT explain why the ones place doesn't change when they repeatedly add 10.

The CCSS emphasizes that students should be able to mentally add and subtract 10, without having to count. Help students develop a conceptual understanding of repeatedly adding 10s in this lesson-this promotes mental math!

5 minutes

**CCSS Context:**

1.NBT.C.5 calls for students to mentally find 10 more and 10 less. Not only are students expected to do this without counting, they have to be able to explain the reasoning used-which means they can't just memorize it! This lesson build the conceptual understanding necessary for students to understand what is happening when they add 10 repeatedly, and to notice the pattern that will help them solve these problems mentally. See attached video to hear how this complex task is matched with the standard.

**Review past learning: **

Yesterday we solved a problem where we repeatedly added 10 toys to Andy's toy box. Today we are going to think again about what is happening when we repeatedly add 10, focusing on why the ones place stays the same.

**Connect to the Real World:**

In 2nd grade, you are going to have to add 10 and 100 to a number without counting, in 3rd grade, you'll add 1000 without counting! Understanding why the ones place doesn't change will help you when you add bigger numbers later.

**Objective: ****Your thinking job is: When I add 10, why doesn't the ones place change?**

15 minutes

**Present Task: **We are going to make a 10 More Book today-in your book you will show how you add 10 over and over to your number. We will focus specifically on how the number in the tens place changes and how the number in the ones place changes.

**To model how to use the book, I will show them how to make a 10 more book whole group. I'll use an enlarged version of what their booklets look like (see template in the next section; I just blow this template up on the copy machine and use the enlarged version in my model).**

I'll have one student use a base 10 model in front of the class to model the process of adding 10 as we go through the process together and I model how to use the booklet. What is tricky is that students have to take the number from the previous page and add 10 to that number. This is most difficult when they have to turn the page-this is a 6 year old's quantum mechanics! Modeling how I transfer the number to each new page will help students easily use the booklet.

**My Start number: 28**

**Focus Question as we add 10:**

- How is the number of 10s and 1s changing? Do you notice a pattern?
*This question primes students for MP8, Look for and express regularity in repeated reasoning. We will revisit this in the student debrief.*

15 minutes

Each student makes an Adding 10 Booklet. I will give them a start number, and then they will add 10 repeatedly. On each page, there is a space to record the strategy for adding 10 more, as well as record the number of tens and ones in the new number.

**Group A: Intervention -**These students should use base ten models, and start at a number under 10. They may revert back to adding 10 ones as opposed to adding a group of 10. If that happens, I'll ask: Is there an easier way to represent adding 10?**Group B: Right on Track -**These students start at a number in the teens. This will insure they go above 100, which helps them start to think about where the ones place is in these numbers also. Students have base 10 blocks available, but may choose a different strategy (number line, hundreds chart, counting)**Group C: Extension -**These students start at a number in the 50s. These students will probably need base 10 models to think about the numbers over 100, so I am anticipating they will switch from mental strategies to base 10 as the numbers increase.

20 minutes

**Class Debrief: **I'll bring students back together, and show one number set that a student in Group B had. I'll have the start number and all of the 10 more numbers listed on a piece of chart paper.

Focus Question: Why didn't the ones place change?

- First, confirm that the ones place in fact did not change with the class. I'll underline the ones place in each group so we can discuss how it stayed constant.
- Scaffold questions:
- What do you notice about the tens place?
- Why did the tens place count up like 1, 2, 3, 4, etc?

I will have base ten models available on the carpet when we discuss this-students will probably want the concrete model to help them explain that the number of ones didn't change when you put another ten down.

**Student Writing: **After we discuss, I'll have students go write why the ones place didn't change on the cover of their adding 10 book. This is aligned to the CCSS shift to writing across the curriculum, and it provides a great summarizer of the day's learning.