Unit Plan 13 (Grade 1 Math): Add 10 More & 10 Less

Focus: Mentally find 10 more and 10 less than a number (within 120) and explain using place value.

Grade Level: 1

Subject Area: Mathematics (Number & Operations in Base Ten)

Total Unit Duration: 5 sessions (one week), 45–60 minutes per session

I. Introduction

Students use place-value structure to reason that adding/subtracting ten changes the tens digit while the ones stay the same. Using hundreds charts, number lines, and base-ten blocks, they move from concrete to mental strategies for 10 more/10 less, including across decades (e.g., 39 → 49/29) and close to 100.

Essential Questions

• How does place value help me find 10 more or 10 less quickly?
• Why does adding/subtracting 10 change the tens but not the ones?
• How can a hundreds chart, number line, or base-ten blocks prove my answer?

II. Objectives and Standards

Learning Objectives — Students will be able to:

1. Describe 10 more/10 less using tens and ones language.
2. Use hundreds charts, number lines, and base-ten blocks to model ±10.
3. Find 10 more/10 less mentally for numbers within 120, including across decades.
4. Explain and justify results with place-value reasoning and representations.

Standards Alignment — CCSS Grade 1 (threaded across the unit)

• 1.NBT.5: Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.
• Mathematical Practices: MP.7 (Look for and make use of structure) emphasized; MP.6/MP.2 threaded.

Success Criteria — Student Language

• I can tell 10 more/10 less by looking at the tens and ones.
• I can prove my answer with a hundreds chart, number line, or blocks.
• I can find ±10 mentally and explain why it works.