Unit Plan 7 (Grade 3 Math): Addition/Subtraction within 1,000—Methods & Reasoning
Build fluency adding and subtracting within 1,000 by using place-value strategies, compensation, open number lines, and standard algorithms—explaining steps, checking for reasonableness, and critiquing mathematical reasoning.
Focus: Use place-value strategies, properties of operations, and algorithms with explanations to add/subtract within 1,000; justify choices and critique reasoning.
Grade Level: 3
Subject Area: Mathematics (Number & Operations in Base Ten)
Total Unit Duration: 5 sessions (one week), 45–60 minutes per session
I. Introduction
Students strengthen addition and subtraction within 1,000 by connecting decomposing/compose strategies, open number lines, and the standard algorithm. They explain each step with place-value reasoning, evaluate reasonableness, and use error analysis to refine thinking.
Essential Questions
- How do place value and properties help me choose an efficient method for +/– within 1,000?
- What does it mean to explain each step of an algorithm using hundreds–tens–ones?
- How can I tell if an answer is reasonable, and how do I find and fix errors?
II. Objectives and Standards
Learning Objectives — Students will be able to:
- Add and subtract within 1,000 using decomposing, compensation, open number lines, and the standard algorithm.
- Explain the why behind each step using place-value language and properties (e.g., associativity for grouping addends).
- Evaluate solutions for reasonableness via estimation and inverse operations (add ↔ subtract).
- Engage in math talk to defend a method and critique a peer’s reasoning with evidence.
- Use precise labels, organized workspaces, and clear representations.
Standards Alignment — CCSS Grade 3
- 3.NBT.2: Fluently add and subtract within 1000 using strategies and algorithms based on place value, properties of operations, and/or the relationship between addition and subtraction.
- Mathematical Practices: MP.3 (Construct viable arguments and critique the reasoning of others).
Success Criteria — Student Language
- I can choose a strategy (decompose, compensate, open number line, or algorithm) and tell why it fits.
- I can explain each step using hundreds–tens–ones and regrouping when needed.
- I can check my answer with an estimate or the inverse and fix errors I find.