Unit Plan 4 (Grade 2 Math): Odd & Even—Structure and Proofs

Focus: Determine odd/even with models to 20; show even numbers as the sum of two equal addends; justify with simple proofs (pairing, arrays, and “one left over”).

Grade Level: 2

Subject Area: Mathematics (Operations & Algebraic Thinking)

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

I. Introduction

This week, students use pairs, arrays, and ten-frames to decide whether numbers are odd or even and to justify their decision. They learn that even numbers can be written as a double (the sum of two equal addends) and practice giving short because statements to defend their thinking.

Essential Questions

• What makes a number even or odd?
• How can pairing and arrays help me prove my claim?
• How do I write an equation to show an even number as two equal addends?

II. Objectives and Standards

Learning Objectives — Students will be able to:

1. Use pairing (make twos) and ten-frames/arrays to decide if a number to 20 is odd or even.
2. Write an equation showing an even number as the sum of two equal addends (a double).
3. Explain their reasoning with a clear because statement and a matching model.
4. Recognize structure (skip-count by 2s, “one left over”) and use it to check work.
5. Create and critique short proofs (agree/disagree and tell why) using pictures and words.

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

• 2.OA.3: Determine whether a group of objects (up to 20) has an odd or even number of members; write an equation to express an even number as a sum of two equal addends.
• Mathematical Practices: MP.3 (Construct viable arguments & critique reasoning) and MP.7 (Look for & make use of structure) emphasized; MP.6 precision is present in labeling.

Success Criteria — Student Language

• I can make pairs or use an array to show a number is odd/even.
• I can write an equation like 8 = 4 + 4 to show an even number.
• I can prove my answer by saying because and pointing to my model.