Unit Plan 10 (Grade 2 Math): Fluency within 100—Efficient Methods
Add and subtract within 100 using place value, properties, and inverse relationships; choose efficient strategies like make-a-ten or compensation and explain why they work.
Focus: Add/subtract within 100 using place value, properties of operations, and the relationship between addition and subtraction; explain why strategies work.
Grade Level: 2
Subject Area: Mathematics (Number & Operations in Base Ten • Operations & Algebraic Thinking)
Total Unit Duration: 5 sessions (one week), 35–45 minutes per session
I. Introduction
This week builds efficient, accurate computation within 100. Students compare methods (e.g., make a ten, decompose/compose tens and ones, compensation) and use the relationship between +/– to check work. Emphasis is on explaining why strategies work using place value and properties.
Essential Questions
- How can place value help me add and subtract within 100 more efficiently?
- How do the properties (commutative/associative) support my method?
- How does the relationship between addition and subtraction help me check my work and explain why a strategy works?
II. Objectives and Standards
Learning Objectives — Students will be able to:
- Add and subtract within 100 using place-value strategies (compose/decompose tens and ones), properties, and number line/100-chart reasoning.
- Choose an efficient method (e.g., make a ten, near doubles, compensation) and explain why it works with place value or properties.
- Use the relationship between addition and subtraction to check answers and justify solutions.
- Communicate thinking with equations, clear labels, and reasonableness checks.
Standards Alignment — CCSS Grade 2 (spiral across the unit)
- 2.NBT.5: Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.
- 2.NBT.9: Explain why addition and subtraction strategies work, using place value and the properties of operations.
- MP.3: Construct viable arguments and critique the reasoning of others. (MP.1 perseverance and MP.6 precision are reinforced.)
Success Criteria — Student Language
- I can choose a strategy that fits the numbers (e.g., make a ten, compensation, break apart tens/ones).
- I can explain why my strategy works using place value or a property.
- I can check subtraction with addition (and addition with subtraction) and decide if my answer is reasonable.