Unit Plan 12 (Grade 2 Math): Add/Sub within 1,000—Models to Methods

Focus: Use base-ten blocks, drawings, and expanded form to add/subtract within 1,000; connect models to written methods and explain why strategies work.

Grade Level: 2

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

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

I. Introduction

Students develop flexible methods to add and subtract within 1,000 by moving from concrete models to representations and then to written methods. They choose tools strategically (MP.5), make estimates, and justify why their strategies work using place value and properties of operations.

Essential Questions

• How does place value help me add and subtract within 1,000 accurately?
• When should I use models, expanded form, an open number line, or a written method?
• How do I explain why my strategy works, not just how to do it?

II. Objectives and Standards

Learning Objectives — Students will be able to:

1. Add and subtract two- and three-digit numbers within 1,000 using base-ten blocks, drawings, expanded form, and open number lines.
2. Regroup (compose/decompose tens and hundreds) and keep place-value alignment in written methods.
3. Explain why strategies work using place value and properties (relationship between addition and subtraction).
4. Select appropriate tools (MP.5) and check reasonableness with estimation.

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

• 2.NBT.7: Add and subtract within 1,000 using models/strategies based on place value, properties, and the relationship between addition and subtraction; relate the strategy to a written method.
• 2.NBT.9: Explain why addition and subtraction strategies work using place value and properties.
• MP.5: Use appropriate tools strategically.

Success Criteria — Student Language

• I can decompose numbers by hundreds/tens/ones, regroup when needed, and align place values.
• I can show my work with a model or representation and a written method that match.
• I can explain why my method works (using place value and the relationship between addition and subtraction) and check with an estimate.