Students will be able to add two-digit numbers with and without regrouping using a model.
Introduction (5 minutes)
- Stimulate classroom engagement by asking your students if any of them like M&Ms. Let them know that this lesson involves adding numbers using M&Ms.
- Direct students' attention to the key at the bottom of the M&M place value mat, which states that 10 blue M&Ms are equivalent to one red M&M.
- Show them the rest of the place value mat. Explain that each blue M&M equals one and belongs in the ones place, or the number position one space left of a decimal point. Each red M&M equals ten and belongs in the tens place, or number position two spaces to the left of a decimal point.
- Inform the class of this important rule: There cannot be more than nine M&Ms in any column.
Explicit Instruction/Teacher Modeling (15 minutes)
- Display the Place Value Mat using a whiteboard or projector, making it visible to the entire class.
- Show your students how to use the place value mat. For example, write a small number (like 24) on the board. Denote 24 on the place value mat by placing two red M&Ms in the tens place and four blue M&Ms in the ones place.
- Underneath 24, write "+2."
- Have a student come up to add two on the mat. She should place two more blue M&Ms into the ones place.
- Ask students to tell you what they think the new value is, and then explain the correct answer. For the current example, inform them that the correct answer is 26 because there are two M&Ms in the tens place and 6 M&Ms in the ones place.
- Next, give them a trickier challenge. Write "15" on the board and ask for a student to denote 15. She should place 1 red M&M in the tens place and one five blue M&Ms in the ones place.
- Underneath 15, write "+6."
- Have another student come up to add six to the mat.
- If she places six more blue M&Ms into the ones place, remind the class that there can't be more than nine M&Ms in any column. Pose the question: Since the ones place has more than nine M&Ms, we need to get rid of some. How can we remove M&Ms from the ones place without changing the number?
- Accept responses from the class. If needed, remind students of the key at the bottom of the mat.
- Explain that the solution involves replacing 10 blue M&Ms with one red M&M. Demonstrate this by removing 10 blue M&Ms from the ones place and adding one red M&M to the tens place. Explain that this process is called regrouping.
- Ask students questions to guide them toward the current number. For example, ask: How many M&Ms are in the tens place now? How many M&Ms are in the ones place now? What number do they make altogether?
- Repeat this demonstration with three more addition problems, two of which should require regrouping.
Guided Practice/Interactive Modeling (20 minutes)
- Have students wash or sanitize their hands.
- Distribute the bags of M&Ms and place value mats.
- Partner up the students. Announce the first problem, such as 83 + 5. Have each pair work together to model the problem and determine an answer.
- Walk around and assist those who seem to be struggling.
- Once most pairs have finished, review the correct answer as a class. Have a volunteer explain how she and her partner arrived this answer.
- Repeat this activity with three more addition problems, two of which should require regrouping.
Independent Working Time (10 minutes)
- Give students two problems to complete independently on their place value mats, such as 62 + 8 and 84 + 9.
- Have them write down their answers on a notecard or piece of scrap paper and turn them in when done.
- Review the two problems as a class.
- Enrichment: Students who complete the practice problems quickly can be challenged with problems that require the addition of two 2-digit numbers without a multiple of 10 (e.g. 18 + 32). You could also ask these students to complete subtraction problems that require regrouping (e.g. 44 - 6).
- Support: During partner work, it could be helpful to pair students who need extra support with those who have a strong understanding of place value concepts. You can also give them extra practice problems that don't require regrouping. This would help them better understand the ones and tens places.
Assessment (5 minutes)
- Examine the answers that each student submitted in order to assess her understanding of regrouping. Two common errors to look for are: no regrouping and partial regrouping. For example, consider 84 + 9. If a student's answer to this problem is 813, then she likely kept 13 in the ones place and didn't regroup. If a student's answer is 83, then she likely removed 10 from the ones place, but didn't add 10 to the tens place.
Review and Closing (5 minutes)
- Reward your students' hard work by allowing them to eat some M&Ms. Depending on the condition of the M&Ms they were working with, you may want to give them new packs instead.
- Have students discuss their definition of the word "regroup" as they enjoy their M&Ms.
- Ask some students to share their definitions. As a class, come up with a definition to use for the remainder of the place value unit.