Unit Plan 15 (Grade 4 Math): Measuring Angles—Protractors in Action
Measure and sketch angles in whole-number degrees using a protractor, connect angles to rotation, and use right/straight benchmarks to estimate and justify accuracy.
Focus: Measure and sketch angles in whole-number degrees; connect to rotations and benchmarks for right and straight angles.
Grade Level: 4
Subject Area: Mathematics (Measurement & Data—Angles • Geometry connection)
Total Unit Duration: 5 sessions (one week), 45–60 minutes per session
I. Introduction
Students learn to see an angle as a rotation of one ray about a vertex, then use a protractor to measure and sketch angles in whole-number degrees. They estimate using benchmarks (quarter-turn/right angle; half-turn/straight angle) and justify their measurements with clear setup and markings.
Essential Questions
- How do I set up a protractor so my measurement is accurate?
- How can benchmarks (right/straight angles) help me estimate before measuring?
- Why is an angle about rotation, not the length of its rays?
II. Objectives and Standards
Learning Objectives — Students will be able to:
- Explain an angle as the rotation between two rays with a common vertex.
- Place a protractor correctly (center on vertex, baseline aligned with one ray) and choose the correct scale.
- Measure and record angle size in degrees (°) with appropriate symbols/labels.
- Sketch angles from a given degree measure using benchmarks and ray construction.
- Estimate angle size using right/straight angle benchmarks and justify reasonableness.
Standards Alignment — CCSS Grade 4 (spiral across the unit)
- 4.MD.5: Recognize angles as geometric shapes formed by two rays with a common endpoint; understand angle measure in degrees.
- 4.MD.6: Measure and sketch angles in whole-number degrees using a protractor; read angle measures in diagrams.
- Connections: 4.G.1 (angle types) and preview of 4.MD.7 (angle composition) as informal supports; MP.1–MP.8 threaded.
Success Criteria — Student Language
- I can set my protractor with the center on the vertex and the baseline on a ray.
- I can pick the right scale, read, and record an angle in degrees (°).
- I can sketch a given-degree angle and explain why my measurement is reasonable.