Unit Plan 26 (Grade 2 Math): Computation Routines—Within 100 & 1,000

Focus: Daily computation strings strengthen mental math, compensation, and regrouping connections across place value; students explain why strategies work and check for reasonableness.

Grade Level: 2

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

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

I. Introduction

This week builds flexible, efficient computation through short, daily “number strings.” Students connect mental strategies (make a ten, add tens/hundreds, compensation) to written methods with regrouping. Emphasis is on clear explanations of why strategies work and consistent self-checking.

Essential Questions

• How can I use place value to make a problem easier (without changing the value)?
• When should I use compensation or regrouping, and how do I know my answer is reasonable?
• Why do addition and subtraction strategies work?

II. Objectives and Standards

Learning Objectives — Students will be able to:

1. Add and subtract within 100 using place-value strategies, properties, and relationships between operations.
2. Add and subtract within 1,000 using models and written methods that involve regrouping; explain steps.
3. Mentally add or subtract 10 or 100 from a number 100–900 and justify the result using place value.
4. Choose and describe efficient strategies (make a ten, compensation, decompose/recompose) for a given problem.
5. Explain why strategies work using place-value reasoning and properties of operations.

Standards Alignment — CCSS Grade 2 (focus this week)

• 2.NBT.5: Fluently add/subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.
• 2.NBT.7: Add/subtract within 1,000 using concrete models or drawings and strategies based on place value; relate strategies to a written method (including regrouping).
• 2.NBT.8: Mentally add/subtract 10 or 100 to/from a given 100–900 number; explain reasoning.
• 2.NBT.9: Explain why addition and subtraction strategies work, using place value and properties of operations.
• Mathematical Practices: MP.8 emphasized (notice/use regularity); MP.1, MP.3, MP.6, MP.7 threaded.

Success Criteria — Student Language

• I can choose a strategy (make a ten, add tens/hundreds, compensation) and tell why it fits.
• I can show and explain my regrouping steps so someone else can follow.
• I can do quick mental changes of +10/–10 or +100/–100 and tell what changed (hundreds/tens/ones).
• I can check my answer by using the opposite operation or a friendly estimate.