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👩‍🏫 Teaching Guide • Grade 1

How to Teach Subtraction within 20

Subtraction becomes more flexible in Grade 1 when students learn that it is not just taking away. This guide helps children use number lines, fact families, and comparison language with confidence.

📐 Standards Alignment

1.OA.A.1 CCSS.MATH

Use addition and subtraction within 20 to solve word problems.

1.OA.B.4 CCSS.MATH

Understand subtraction as an unknown-addend problem.

1.OA.C.6 CCSS.MATH

Add and subtract within 20 using counting, number lines, and related facts.

📦 Materials Needed

  • Number line 0-20
  • Counters
  • Ten-frame cards
  • Story problem cards

🎯 Teaching Strategies

💡
Model Taking Away First Use counters so students can physically remove items and see what remains before moving to equations.
💡
Connect Subtraction to Addition Show related facts side by side so students notice that the same three numbers can make both addition and subtraction equations.
💡
Teach Comparison Language Use questions like "How many more?" and "How many fewer?" so subtraction is not limited to take-away stories.

⚠️ Common Misconceptions

❌ Misconception: Students count the starting number as the first move back

✅ Correction: Have them place a finger on the starting number, then move before saying the first number back.

❌ Misconception: Students think subtraction always makes zero or a tiny number

✅ Correction: Use examples like 20 - 1 to show that the answer can still be large.

📊 Differentiation Tips

Struggling

Keep the starting number at 10 or below until count-back is secure.

On-level

Mix equation practice with picture and story problems so students choose the strategy that fits.

Advanced

Ask students to explain two ways to solve the same subtraction problem.

🚀 Extension Activities

  1. Sort story problems into addition and subtraction groups.
  2. Build fact-family triangles with three numbers.
  3. Play subtraction bowling with plastic cups and a soft ball.