Unit Plan 32 (Grade 2 Math): NBT Problem Solving—100s, 10s, and 1s

Focus: Targeted tasks to solidify 2-digit and 3-digit addition/subtraction and mental 10s/100s shifts using place-value reasoning.

Grade Level: 2

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

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

I. Introduction

Students strengthen computation with hundreds–tens–ones by using compose/decompose, compensation, and open number lines. Daily problem strings and error analysis push flexible thinking, while quick mental 10s/100s shifts build fluency and number sense.

Essential Questions

• How does place value help me choose an efficient strategy for addition/subtraction?
• When should I solve mentally (add/sub 10 or 100) and when should I use a model or written method?
• How do I check reasonableness (estimate, inverse operations, compatible numbers)?

II. Objectives and Standards

Learning Objectives — Students will be able to:

1. Add/subtract within 100 using place-value strategies, properties, and the relationship between addition and subtraction.
2. Add up to four two-digit numbers using efficient grouping (friendly 10s) and explain choices.
3. Add/subtract within 1,000 using base-ten models, drawings, and open number lines; connect steps to place value.
4. Make mental 10s/100s shifts (e.g., 267 + 100, 542 − 10) and explain why the digit(s) change.
5. Explain why strategies work using place value and properties; identify and correct common errors.

Standards Alignment — CCSS Grade 2 (focus this week)

• 2.NBT.5: Fluently add/subtract within 100 using place value, properties, and relationship between +/–.
• 2.NBT.6: Add up to four two-digit numbers.
• 2.NBT.7: Add/subtract within 1,000 using models/drawings and strategies; relate to a written method.
• 2.NBT.8: Mentally add/subtract 10 or 100 to a given number 100–900.
• 2.NBT.9: Explain why addition/subtraction strategies work.
• Mathematical Practices: MP.7 (look for/use structure) featured; MP.1, MP.3, MP.6 supported.

Success Criteria — Student Language

• I can do +10/–10 or +100/–100 in my head and tell why it works.
• I can show compose/decompose or compensation with a model (blocks or open number line).
• I can check my answer by estimating or using the inverse operation and fix mistakes.