Mathematics · 1st Grade

Active learning ideas

Subtracting Multiples of Ten

Active learning works for this topic because subtracting multiples of ten relies on students visualizing how only the tens digit changes while the ones digit stays the same. Concrete materials and collaboration help students internalize this abstract idea by making the invisible remain visible.

• Common Core State Standards
• CCSS.Math.Content.1.NBT.C.6

• 15–25 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Think-Pair-Share
• 15 min · Pairs

Think-Pair-Share: What's Left in the Ones?

Present 63 - 40. Partners individually predict the result and specifically predict what the ones digit will be before solving. They share predictions, then use a hundreds chart or base-ten blocks to verify. The class discusses why every pair got the same ones digit even when their solving strategies differed.

Explain how subtracting a multiple of ten only affects the tens digit.

Facilitation Tip

During Think-Pair-Share, circulate and listen for students who notice the ones digit stays the same, then invite them to share their observation with the class.

What to look for

Give students a card with a problem like '60 - 30 = ?' and '75 - 20 = ?'. Ask them to write the answer and circle the digit that changed in the second problem. Then, ask them to write one sentence explaining why the other digit did not change.

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Activity 02

• Inquiry Circle
• 20 min · Small Groups

Inquiry Circle: Rod Removal

Groups build a two-digit number with rods and unit cubes. One student removes a specified number of rods (e.g., 3 rods for subtracting 30) while another watches the units and confirms they never change. The group records the before and after numbers and writes the equation.

Predict the result of subtracting 10 or 20 from a given two-digit number.

Facilitation Tip

In Rod Removal, remind students to verbalize what they see happening to the rods and unit cubes as they physically remove them.

What to look for

Display a number on the board, such as 48. Ask students to hold up fingers to show how many tens they would subtract (e.g., 1, 2, or 3). Then, ask them to write the resulting number on a mini-whiteboard and hold it up. Discuss the ones digit for each result.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 03

• Gallery Walk
• 20 min · Pairs

Gallery Walk: Hundreds Chart Trails

Post hundreds charts with a start number circled. Students visit each chart, draw arrows moving up the specified number of rows to subtract a given multiple of ten, and write the equation. Pairs compare charts and discuss why moving up on the hundreds chart subtracts tens.

Design a mental strategy for subtracting multiples of ten.

Facilitation Tip

For Hundreds Chart Trails, ask students to point to each number they land on and explain why the ones digit didn't change.

What to look for

Pose the question: 'Imagine you have 50 blocks. You take away 20 blocks. How many are left? Now, imagine you have 58 blocks and you take away 20 blocks. How many are left? What is the same about these two problems?' Facilitate a discussion about the role of the ones digit.

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

Activity 04

• Stations Rotation
• 25 min · Small Groups

Stations Rotation: Mental Subtraction Ladders

At each station a ladder shows a starting two-digit number. Students subtract a given multiple of ten at each rung and write the result, varying the multiple (10, 20, 30) and starting number across stations. Students explain their mental strategy aloud to a partner before writing the answer.

Explain how subtracting a multiple of ten only affects the tens digit.

Facilitation Tip

At Mental Subtraction Ladders, challenge students to explain their jumps aloud before writing the answer to reinforce place-value reasoning.

What to look for

Give students a card with a problem like '60 - 30 = ?' and '75 - 20 = ?'. Ask them to write the answer and circle the digit that changed in the second problem. Then, ask them to write one sentence explaining why the other digit did not change.

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

A few notes on teaching this unit

Teachers should emphasize place value by modeling subtraction with base-ten blocks first, then transitioning to mental math. Avoid teaching subtraction as a digit-by-digit process, which can reinforce misconceptions. Research suggests that students benefit from repeated exposure to visual models before abstract symbols, so rotate materials until the concept clicks.

Successful learning looks like students confidently subtracting multiples of ten while explaining that the ones digit remains unchanged. They should use place-value language to describe their process and correct peers when they notice the ones digit shifting.

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Watch Out for These Misconceptions

• During Collaborative Investigation: Rod Removal, watch for students who remove both rods and unit cubes when subtracting a multiple of ten.

  Have students physically remove only the rods while keeping the unit cubes in place, then ask them to count the remaining blocks to see the ones digit stayed the same.

• During Think-Pair-Share: What's Left in the Ones?, watch for students who think the ones digit cannot stay the same if the tens digit is too small.

  Use rods to show that removing 2 rods from 2 rods leaves 0 tens, while the 3 unit cubes remain untouched, proving the ones digit doesn’t depend on the tens digit.

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Methods used in this brief

• Think-Pair-Share
• Inquiry Circle
• Gallery Walk
• Stations Rotation