Unit Plan 9 (Grade 2 Math): Add/Subtract Lengths—Number Line Models

Focus: Solve length word problems within 100 using number line models with equal units; represent sums and differences with clear jumps, endpoints, and unit labels.

Grade Level: 2

Subject Area: Mathematics (Measurement & Data • Operations)

Total Unit Duration: 5 sessions (one week), 35–45 minutes per session

I. Introduction

This week students turn measurements into models: they use the number line to add and subtract lengths with equal units, show how much longer/shorter, and write matching equations. Emphasis is on accurate units, clear jumps, and reasonableness checks.

Essential Questions

• How does a number line help me add and subtract lengths?
• Why must jumps be equal units and labeled?
• How do I decide if an answer is reasonable for a within 100 length problem?

II. Objectives and Standards

Learning Objectives — Students will be able to:

1. Represent addition and subtraction of lengths on a number line using equal-unit jumps and clear endpoints.
2. Solve one- and two-step length word problems within 100 and write matching equations with an unknown (e.g., 37 + □ = 84).
3. Explain how much longer/shorter by showing the difference on a number line and with computation.
4. Check reasonableness using benchmarks, estimation, and unit sense.

Standards Alignment — CCSS Grade 2 (spiral across the unit)

• 2.MD.5: Use addition and subtraction within 100 to solve word problems involving lengths given in the same units.
• 2.MD.6: Represent whole-number sums and differences within 100 on a number line diagram with equally spaced units.
• 2.OA.1: Solve one- and two-step problems using drawings and equations with a symbol for the unknown.
• MP.4: Model with mathematics (number line, equations). (MP.1 and MP.6 are reinforced through perseverance and precision.)

Success Criteria — Student Language

• I can show my adding/subtracting on a number line with equal jumps and unit labels.
• I can write an equation with an unknown that matches my model.
• I can explain how much longer/shorter by showing the difference on the number line and by computing.
• I can check if my answer is reasonable for a within 100 problem.