Using base-ten blocks, students will create regrouping strategies for numbers. Students are going to: 
- Apply their knowledge of ten and twenty to the addition and subtraction of decade numbers. 
- Reach decade numbers, break down the numbers 1–10.

- How are mathematical representations of relationships made? 
- How can the study of mathematics aid in clear communication?
- How can identifying regularity or repetition help with problem-solving efficiency?
- How do we represent, compare, quantify, and model numbers using mathematics? 
- What does it mean to analyze or estimate a numerical quantity? 
- What qualifies a tool or approach as suitable for a particular task?

- Decompose: Breaking numbers apart (subtraction). 
- Making Ten: Combinations of 10: 9+1, 8+2, 7+3, etc.

- base-ten blocks for each group/pair 
- copies of Regrouping Math worksheet (M-1-2-1_Regrouping Math and KEY)

- Student progress will be assessed through observations made during small-group work, student interaction, and whole-class discussion. 
- Students' comprehension can be evaluated using the Regrouping Math worksheet (M-1-2-1_Regrouping Math and KEY).

Explicit instruction, modeling, scaffolding, and active engagement 
W: Present a set of base-ten blocks to the class and instruct them to tell their math partner everything they know about them. 
H: Explain to the class that they will be adding one- and two-digit numbers with the blocks. 
E: Prior knowledge of structures 10 and 20 will be beneficial. Discuss the divisions and combinations of 10 and 20, and inquire with the students about how this aids in handling higher decade numbers. 
R: Permit students to work in pairs on both their independent practice and the class discussion/exploration. 
E: Select well-understood groups to present at the conclusion. 
T: Assign students a similar task to solve a mental math problem for a specified goal number on a daily or frequent basis. Before moving on to larger decades, students can work in small groups to practice making 10 using base-ten frames and cubes if they need more practice. 
O: The purpose of this lesson is to teach students how to break down numbers 2 through 9 and to recognize place value. 

"We refer to these as base-ten blocks." Assign a student to count how many cubes there are in one of the tens. Next, assist your students in saying that each of the tens contains ten ones or cubes. Show how 10 ones are equal to one 10 using an overhead or document camera. 

"How many would I have in total if I had six ones and three ones?" Invite students to share their ideas. "How many would I have overall if I had six ones and four ones?" Encourage discussion among the students. Permit someone to speak up who mentions that you can have one ten or ten ones. Then pose the question, "How many would I have overall if I had six and added six more?" After a partner discussion, call on a few who raised various points. To illustrate, let's say you had two extra ones after trading in six ones and four ones for a ten. Create a numerical sentence to demonstrate to the class that 6 + 4 = 10.

Repeat the process with a larger decade number. "How many cubes would I have if I had one ten and eight ones?" Ask the class to respond as a whole. "If I added four more ones, how many would I have?" After a discussion among partners, call on a few individuals who raised various points. "I could combine the 8 ones and 2 ones to make another ten; then I'd have two extra ones," was one possible response. "I would therefore have 22." 

Continue doing this until the majority of students appear to understand regrouping well.

Distribute copies of M-1-2-1_Regrouping Math and KEY, the worksheet for regrouping math.

Allow students to work in pairs to talk about the methods they employ to regroup the ones into tens. Make sure that students who require or desire them have access to real base-ten blocks. Observe who struggles to reorganize into a hundred. 

Make a group call for the class once everyone has completed their sheet. Select a handful of the issues that caused greater difficulty for the students. Pick one or two pairs and discuss each other's approaches. 

Extension:

Throughout the year, adapt the strategies and activities listed below to your students' needs.

Routine: As a calendar routine, students can use base-ten blocks to build the date's number. "How many will we have four days from now?" you might ask.

Small Group: Unifix cubes are a good starting point for students who may require opportunities for additional learning because of their ease of manipulation. In towers of ten cubes, five of each of two distinct colors should be present. In this manner, if students have two towers of 10 and 5 red and 1 blue, they can see that 4 more blue towers are needed to have an additional 10. They could see they would need two red and five blue cubes, or a total of seven cubes, to have another ten if they had two towers of ten and three red.

Expansion: When they're ready, students can use the base-ten blocks to practice subtracting one-digit numbers from two-digit numbers. Once more, to make manipulation easier, you might need to have some tens composed of ten ones already assembled.