Subtraction within 20Activities & Teaching Strategies
Active learning transforms subtraction within 20 from abstract symbols into concrete understanding. When students manipulate objects, partner with peers, and dramatize situations, they see how numbers break apart and recombine, turning rote counting into flexible thinking. These hands-on experiences build the mental models that make mental math possible.
Learning Objectives
- 1Calculate the difference between two numbers within 20 using number bonds.
- 2Apply the make-ten strategy to solve subtraction problems within 20.
- 3Explain how addition can be used to check the accuracy of subtraction answers within 20.
- 4Represent subtraction problems within 20 using concrete manipulatives.
- 5Identify the unknown part in a subtraction number bond.
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Pair Work: Number Bond Subtraction Cards
Prepare cards with subtraction problems within 20 and blank number bonds. Pairs draw a problem, draw the bond to decompose, solve using make-ten if needed, and check by adding. Switch cards every 3 minutes and discuss strategies.
Prepare & details
How can we use number bonds to help us subtract teen numbers?
Facilitation Tip: During Pair Work: Number Bond Subtraction Cards, circulate and ask each pair to verbalize their number bond before solving the subtraction problem, ensuring they connect the parts to the whole.
Setup: Standard classroom seating; students turn to a neighbor
Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs
Small Groups: Make-Ten Counter Challenge
Give each group counters and ten-frames. One student poses a subtraction like 17 - 8; others model making ten on the frame, subtract the rest, and verify with addition. Rotate roles after two problems.
Prepare & details
What strategies can we use when we subtract from a teen number?
Facilitation Tip: During Small Groups: Make-Ten Counter Challenge, watch that students physically move counters into groups of ten before subtracting the remaining amount, reinforcing the decomposition process.
Setup: Standard classroom seating; students turn to a neighbor
Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs
Whole Class: Subtraction Story Dramatization
Read a story problem aloud, such as '18 apples, eat 9'. Class uses personal counters to act out number bonds and make-ten steps on desks, then shares answers chorally and checks with addition.
Prepare & details
How does addition help us check our subtraction?
Facilitation Tip: During Whole Class: Subtraction Story Dramatization, invite students to act out the story while you record their actions as equations on the board, linking movement to symbolic representation.
Setup: Standard classroom seating; students turn to a neighbor
Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs
Individual: Strategy Choice Boards
Provide boards with 8 problems within 20. Students choose number bonds or make-ten for each, draw their work, and add back to check. Circulate to prompt explanations.
Prepare & details
How can we use number bonds to help us subtract teen numbers?
Setup: Standard classroom seating; students turn to a neighbor
Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs
Teaching This Topic
Teachers approach subtraction within 20 by first anchoring the work in concrete tools, then scaffolding toward mental strategies. Avoid rushing to abstract symbols before students can explain their moves with objects or drawings. Research shows that students who can decompose numbers flexibly in first grade perform better in later math, so prioritize verbal explanations over speed. Use consistent language like ‘make ten’ and ‘take apart’ to build a shared mental model across activities.
What to Expect
Success looks like students choosing the make-ten strategy over counting one-by-one, explaining their steps with number bonds, and verifying answers independently. You will notice students moving from slow, single-count strategies to efficient decompositions, and explaining their work with phrases like ‘take apart 11 into 10 and 1’ without prompting.
These activities are a starting point. A full mission is the experience.
- Complete facilitation script with teacher dialogue
- Printable student materials, ready for class
- Differentiation strategies for every learner
Watch Out for These Misconceptions
Common MisconceptionDuring Pair Work: Number Bond Subtraction Cards, watch for students who skip the number bond step and count back one-by-one from the minuend.
What to Teach Instead
Prompt the pair to build the minuend with counters and circle the group of ten before removing any. Ask them to name the parts aloud before writing the equation, reinforcing the bond structure.
Common MisconceptionDuring Small Groups: Make-Ten Counter Challenge, watch for students who remove counters without grouping ten first, treating the counters as single units.
What to Teach Instead
Model splitting the minuend into ten and the rest, then ask the group to agree on the ten-group before removing any counters. Have them say the split aloud as they build it.
Common MisconceptionDuring Whole Class: Subtraction Story Dramatization, watch for students who act out the story but write the equation incorrectly, mixing up minuend and subtrahend.
What to Teach Instead
After the dramatization, ask the class to identify the starting amount and the amount removed before recording. Use gestures to connect the action to the equation.
Assessment Ideas
After Pair Work: Number Bond Subtraction Cards, display a number bond template for 14 on the board. Ask students to fill in the parts (e.g., 10 and 4) and solve 14 - 6 using their cards. Collect a sample set to check for correct decomposition and subtraction steps.
After Small Groups: Make-Ten Counter Challenge, give each student a card with a problem like 17 - 8. Ask them to write the number bond for 17, solve using make-ten, and write an addition check. Review tickets to assess strategy choice and verification.
During Whole Class: Subtraction Story Dramatization, pause the story and ask, ‘How can we use the make-ten strategy to find how many are left?’ Listen for students to describe breaking apart the minuend and subtracting from ten first, then the rest.
Extensions & Scaffolding
- Challenge: Present mixed problems (e.g., 18 - 9, 14 - 6) on a choice board with a timer. Students solve two using any strategy and two using only the make-ten method, then compare times to see efficiency gains.
- Scaffolding: For students struggling with make-ten, provide counters and a ten-frame mat. Ask them to build the minuend, circle a group of ten, then remove the subtrahend, counting what remains.
- Deeper: Extend the Make-Ten Counter Challenge by asking students to create their own subtraction problems for peers, using the counters to model solutions before swapping cards.
Key Vocabulary
| Subtraction | Taking away a number or quantity from another number or quantity. It is the inverse operation of addition. |
| Number Bond | A visual representation showing the relationship between a whole number and its parts. For subtraction, the whole is at the top and the parts are at the bottom. |
| Make-Ten Strategy | A strategy for subtraction where you first subtract from a teen number to reach 10, then subtract the remaining amount. |
| Part | One of the numbers that make up a whole in a number bond. In subtraction, the parts are the subtrahend and the difference. |
| Whole | The total amount in a number bond. In subtraction, the whole is the minuend, the number from which another number is subtracted. |
Suggested Methodologies
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