Adding 2-Digit Numbers with Regrouping

Regrouping in two-digit addition requires students to move beyond counting by ones and see numbers as flexible groups of tens and ones. Active, hands-on tasks help them build mental images of exchanging ten ones for one ten or ten tens for one hundred, making the abstract concrete and lasting.

• Primary 2
• Mathematics
• 3 activities
• 20 min–30 min

Learning Objectives

1. Calculate the sum of two 2-digit numbers requiring regrouping of ones into tens.
2. Explain the process of regrouping ones as tens when adding two 2-digit numbers.
3. Demonstrate the addition of two 2-digit numbers with regrouping using place value disks and pictorial representations.
4. Apply the column algorithm to accurately add two 2-digit numbers with regrouping.
5. Estimate the sum of two 2-digit numbers to check the reasonableness of the calculated answer.

Simulation Game

⏱ 30 min·Small Groups

Simulation Game: The Great Exchange Bank

One student acts as the 'Banker' while others are 'Accountants'. Accountants must trade 10 ones for 1 ten disk or 10 tens for 1 hundred disk to solve addition problems, physically moving the pieces across a mat.

Prepare & details

Why do we need to regroup when the ones digits add up to 10 or more?

Facilitation Tip: In The Great Exchange Bank, circulate with a tray of place value disks so you can model exchanges instantly when a student hesitates.

Setup: Flexible space for group stations

Materials: Role cards with goals/resources, Game currency or tokens, Round tracker

• Apply
• Analyze
• Evaluate
• Create
• Social Awareness
• Decision-Making

Peer Teaching

⏱ 20 min·Pairs

Peer Teaching: Regrouping Experts

After a short demo, students work in pairs. One student solves a subtraction problem with regrouping while the other acts as a 'coach', checking each step and asking 'Why did you rename that hundred?' before swapping roles.

Prepare & details

How does the column method help us organise addition with regrouping?

Setup: Presentation area at front, or multiple teaching stations

Materials: Topic assignment cards, Lesson planning template, Peer feedback form, Visual aid supplies

• Understand
• Apply
• Analyze
• Create
• Self-Management
• Relationship Skills

Gallery Walk

⏱ 25 min·Small Groups

Gallery Walk: Error Detectives

Display 'broken' addition and subtraction problems where the regrouping was done incorrectly. Students move in groups to identify the mistake and write a 'prescription' on how to fix it.

Prepare & details

How can we use estimation to check whether our answer is reasonable?

Setup: Wall space or tables arranged around room perimeter

Materials: Large paper/poster boards, Markers, Sticky notes for feedback

• Understand
• Apply
• Analyze
• Create
• Relationship Skills
• Social Awareness

Teaching This Topic

Start with concrete tools like place value disks, then bridge to drawings, and finally to symbols. Always connect written steps to the physical action: when you write a '1' above the tens column, say aloud, 'This 1 means we have exchanged ten ones for one ten.' Avoid rushing to the algorithm before the concept is solid.

What to Expect

Students will confidently explain why regrouping is needed and perform the column addition algorithm accurately, using precise place value language. They will also catch and correct their own or peers' errors when the steps are made visible.

Watch Out for These Misconceptions

Common Misconception

During The Great Exchange Bank, watch for students who move disks without recording the exchange in writing.

What to Teach Instead

Prompt them to pause after each move and write the new digit in the tens column on their whiteboard before continuing, linking the physical action to the symbol.

Common Misconception

During Peer Teaching: Regrouping Experts, watch for students who forget to reduce the tens digit after borrowing.

What to Teach Instead

Have peers point to the crossed-out tens digit and ask, 'What does this mark mean? Why did we cross it out?' This makes the reduction visible and verbal.

Assessment Ideas

Exit Ticket

After The Great Exchange Bank, give each student an exit card with 34 + 28. Ask them to solve it using disks and write one sentence explaining why they needed to regroup the ones.

Quick Check

During Gallery Walk: Error Detectives, present 56 + 17 on the board. Ask students to hold up the correct number of fingers to show how many tens they will carry over after adding the ones column, then reveal the final sum on their mini-whiteboards.

Discussion Prompt

After Gallery Walk, pose the question: 'Imagine you are adding 45 + 37. How can you use estimation to predict if your final answer will be closer to 70, 80, or 90? Turn to your partner and explain your thinking using place value language.'

Extensions & Scaffolding

• Challenge: Ask students to create three different two-digit addition problems with regrouping and solve them using the fewest disks possible.
• Scaffolding: Provide a place value mat with columns labeled 'Tens' and 'Ones' and pre-printed numbers so students can focus on the exchange step without writing.
• Deeper exploration: Have students write their own 'renaming stories' for problems like 68 + 26 to explain the exchange in their own words.

Key Vocabulary

Regrouping	Exchanging ten ones for one ten, or ten tens for one hundred, to make it easier to perform addition or subtraction.
Place Value	The value of a digit based on its position within a number, such as ones, tens, or hundreds.
Column Algorithm	A method of adding numbers by writing them vertically in columns according to their place value, aligning ones, tens, and hundreds.
Carry Over	The digit that is moved from one place value column to the next higher place value column during addition when the sum of the digits in a column exceeds nine.