Regrouping Rescue Teacher Guide Regrouping Rescue
Teacher Facilitation Guide • Grade 2 Math
Learning Objective
Students will be able to identify, explain, and correct errors in regrouping by applying the base-10 rule: "10 ones can be replaced with 1 ten."
Timing
Warm-up: 5 min
Video: 5 min
Activity: 20 min
Closure: 5 min
1
Warm-Up: The Ones House Mystery (5 min)
Display Slide 2 showing a Place Value Chart with 15 ones in the ones column.
Prompt:
"Detectives, look at this picture. Something isn't right in the Ones House. What is wrong with this picture?"
Listen for students noticing that only digits 0-9 can live in a column, or that there are "too many" ones.
2
Video & Discussion (5 min)
Watch "Addition to 20 With Regrouping". Use these pause points:
0:49 Pause: "Is it okay to have 12 blocks in the ones house? What is the rule about how many can live there?"1:05 Prediction: "What is going to happen to these 10 blocks? What can we trade them for?"1:15 Connection: "Why did the block change shape? Why did it move to the other side?"
3
Activity: Error Analysis (20 min)
Distribute the Error Analysis Task Cards . Students must solve the "case" for each card:
The Mission:
Identify the error in the regrouping.
Explain in writing WHY it is wrong (using the video logic).
Draw the correct way using base-10 representations.
Common Misconceptions:
Writing the whole sum in the ones place.
Forgetting to add the regrouped ten.
Regrouping when total is less than 10.
4
Closure (5 min)
Have students share their best "explanations" from the activity. Record the "Golden Rule" on an anchor chart:
"When we have 10 ones, we trade for 1 ten!"
Error Analysis Answer Key
Case #1
The Double Digits
Problem: 8 + 4 = 12 (Written as 12 in the ones column)
The Error: Student wrote both digits in the ones place. They forgot the rule that 10 ones must be traded for 1 ten.
Case #2
The Forgotten Tens
Problem: 15 + 6 = 11
The Error: Student added the ones (5+6=11) but completely ignored the existing ten from '15' and the new regrouped ten.
Case #3
The Fake Regroup
Problem: 4 + 4 = 18
The Error: Student "carried the one" even though 4+4 is only 8. You only regroup when you have 10 or more ones!
Case #4
The Great Flip
Problem: 9 + 6 = 51
The Error: Student added 9+6=15, but put the 5 (ones) in the tens place and the 1 (ten) in the ones place. Values are swapped.
Materials Check
Ensure each student has:
Error Analysis Task Cards
Base-10 blocks (cubes and rods)
Reflection Journal Page
Pencil and Eraser (Detectives make mistakes too!)
Regrouping Rescue Slides Top Secret: Math Mission
Regrouping
Rescue
The Case of the Misplaced Ones
Grade 2 • Math Detectives
Warm-Up Mystery
Tens
Ones
"Something isn't right in the Ones column...
What is wrong with this picture?"
Detective Hint:
How many ones are allowed to live in this house?
Investigation: The Rule
Embedded media
Watch closely for the "Magic Trade"!
The Golden Rule of Regrouping
10 ONES
1 TEN
"10 ones can be replaced with 1 ten."
Case File: #001
The Suspect Problem:
7
12
"Wait! Look at the answer box!"
?
What's wrong?
The number 12 is sitting in the ones place. We have 10 too many!
✓
The Fix:
Trade those 10 ones for 1 ten and move it to the tens column!
Detective Briefing
Your Mission
1. Spot It
Find the error on the card.
2. Prove It
Write WHY it's wrong.
3. Solve It
Draw it the right way!
Grab your task cards and let's go!
Error Analysis Task Cards Regrouping Rescue
Evidence File: Error Analysis Task Cards
Detective:
Date:
Mission Briefing
These math problems have regrouping errors! For each case: (1) Circle the mistake. (2) Explain WHY it is wrong in the Detective Notes. (3) Show the correct way in the Regrouping Rescue box.
Case #01
8 + 4
12
Detective Notes: Why is it wrong?
Regrouping Rescue: Show the Correct Way
Tens
Ones
Case #02
1 15 + 6
11
Detective Notes: Why is it wrong?
Regrouping Rescue: Show the Correct Way
Tens
Ones
Case #03
1 4 + 4
18
Detective Notes: Why is it wrong?
Regrouping Rescue: Show the Correct Way
Tens
Ones
Case #04
Adding 9 + 6:
TO
9 + 6
51
Detective Notes: Why is it wrong?
Regrouping Rescue: Show the Correct Way
Tens
Ones
Math Detective Agency • Grade 2 Regrouping Unit • Form #99-PV
Regrouping Rescue Journal Prompts Detective Journal
Mission Reflection: Regrouping Rescue
Name:
Date:
1
What is the "Golden Rule" for regrouping ones?
Complete this sentence:
"When I have 10 ones, I must __________________________________________________
____________________________________________________________________________."
2
Imagine a friend says, "I can just write '15' in the ones column." What would you tell them?
3
Detective Sketchpad
Draw a picture of 10 Ones trading themselves for 1 Ten!
Case Closed
