Subtraction of Numbers to 20

Active learning helps students move beyond counting on fingers to mental strategies that build speed and confidence. For subtraction up to 20, hands-on stations and peer discussions make abstract concepts concrete and memorable. Movement and collaboration turn 'doubles' and 'near-doubles' from abstract rules into tools students can use in real time.

• 1st Class
• Foundations of Mathematical Thinking
• 3 activities
• 15 min–40 min

Learning Objectives

1. Calculate the difference between two numbers up to 20 using concrete materials.
2. Represent subtraction problems involving numbers up to 20 on a number line.
3. Explain the meaning of taking away objects from a set to find a difference.
4. Compare the results of subtraction problems solved using different strategies, such as counting back or using a number line.

Stations Rotation

⏱ 40 min·Small Groups

Stations Rotation: The Strategy Circuit

Set up stations for different mental tricks: one for 'Doubles' using mirrors, one for 'Adding 9' (add 10, subtract 1), and one for 'Near Doubles' using ladybird spots. Students rotate and practice each specific mental shortcut.

Prepare & details

What does it mean to take away some objects from a group?

Facilitation Tip: During The Strategy Circuit, place a timer at each station so students practice using doubles and near-doubles under gentle pressure.

Setup: Tables/desks arranged in 4-6 distinct stations around room

Materials: Station instruction cards, Different materials per station, Rotation timer

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

Think-Pair-Share

⏱ 15 min·Pairs

Think-Pair-Share: How Did You Get There?

The teacher presents a problem like 7 + 8. Students solve it mentally, then explain their specific strategy to a partner (e.g., 'I doubled 7 and added 1' or 'I made a ten'). This surfaces different ways of thinking.

Prepare & details

How can you use counters or a number line to find the answer to a subtraction?

Facilitation Tip: In How Did You Get There?, circulate with a clipboard and listen for clear, concise explanations of mental steps.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

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

Simulation Game

⏱ 20 min·Whole Class

Simulation Game: The Human Number Line

Students stand on a large number line. To solve 9 + 6, the '9' student explains how they can 'jump' to 10 first and then add the remaining 5. This physical 'bridging' makes the mental strategy visible and concrete.

Prepare & details

Can you tell a take-away story using objects from the classroom?

Facilitation Tip: For The Human Number Line, step in only if students lose focus or need help aligning jumps with the correct direction.

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

Teaching This Topic

Teach doubles as a gateway to near-doubles: once students know 5+5 quickly, show 5+6 as 5+5 plus one more. Avoid letting students stay in counting-all habits by modeling speed and accuracy yourself. Research shows that frequent, short bursts of practice with immediate feedback build fluency faster than long drills. Use errors as stepping stones by asking, 'What part feels tricky? Can we use a known double to help?'

What to Expect

By the end of the activities, students should solve subtraction problems up to 20 without relying on fingers or tally marks. They will explain their mental steps using doubles or near-doubles and share strategies with peers. Fluency and confidence in mental calculation will be visible in quick, accurate responses during group work.

Watch Out for These Misconceptions

Common Misconception

During The Strategy Circuit, watch for students who still count on fingers or tally marks for every problem.

What to Teach Instead

Redirect them to use the doubles chart at the station to find a related double and adjust by one. Partner with a student who models quick mental use of near-doubles and ask them to share their strategy.

Common Misconception

During The Strategy Circuit, watch for students who limit doubles to numbers below 5.

What to Teach Instead

Set up a base-ten block station where students model doubling 10, 11, and 12, then write the corresponding number sentences. Encourage them to compare patterns with smaller doubles.

Assessment Ideas

Exit Ticket

After The Strategy Circuit, give each student 10 counters. Ask them to show 15 take away 6 using their mental strategy, write the number sentence, and the answer on a slip of paper.

Quick Check

During The Human Number Line, draw a number line from 0 to 20 on the board. Pose a subtraction problem such as 18 - 5 and ask students to demonstrate how to solve it by jumping backward on the line. Note who aligns jumps correctly and who needs a verbal prompt.

Discussion Prompt

After How Did You Get There?, present a scenario: 'There were 11 birds on a branch, and 4 flew away.' Ask students: 'What does it mean to take away the birds? How can we find out how many birds are left?' Listen for explanations using objects, drawings, or number sentences that show understanding of subtraction as removal.

Extensions & Scaffolding

• Challenge students to create their own near-double problems for partners to solve within 10 seconds.
• Scaffolding: Provide a doubles facts chart at each station for reference during timed challenges.
• Deeper exploration: Ask students to explain how doubling 10 is the same as doubling 1 in the tens place, using base-ten blocks as visual support.

Key Vocabulary

Subtract	To take away a number or quantity from another number or quantity.
Difference	The result when one number is subtracted from another.
Take away	To remove a part from a whole; this is a common phrase used to describe subtraction.
Number line	A line with numbers placed at intervals, used to visualize mathematical operations like addition and subtraction.