Unit Plan 29 (Grade 4 Math): Symmetry—Lines that Balance

Focus: Identify lines of symmetry and draw/analyze symmetric figures; connect reflection ideas to clear visual evidence.

Grade Level: 4

Subject Area: Mathematics (Geometry—Symmetry)

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

I. Introduction

Students learn to spot and justify reflection (line) symmetry in two-dimensional figures. They test shapes using a fold test, trace with patty paper, and use grid/dot paper to reflect points across a mirror line. Emphasis is on evidence (matching corresponding parts) and precise vocabulary.

Essential Questions

• What makes a line a line of symmetry?
• How can I prove two halves are congruent and corresponding across a mirror line?
• How does using tools (folding, tracing, grids) improve the precision of my symmetry decisions?

II. Objectives and Standards

Learning Objectives — Students will be able to:

1. Identify line-symmetric figures and locate valid lines of symmetry using visual tests and tools.
2. Draw accurate lines of symmetry on given figures and reject invalid lines with reasons.
3. Complete a figure to make it symmetric across a given mirror line using corresponding points.
4. Explain and justify symmetry claims using evidence (folds, traces, tick marks, equal distances).
5. Use precise vocabulary (e.g., line of symmetry, reflect, corresponding, congruent) in oral/written explanations.

Standards Alignment — CCSS Grade 4

• 4.G.3: Recognize a line of symmetry for a two-dimensional figure as a line across the figure such that the figure can be folded along the line into matching parts; identify line-symmetric figures and draw lines of symmetry. (Connections: 4.G.1 for line/angle language; 4.MD.6–7 for measuring/checking right angles when relevant.)

Success Criteria — Student Language

• I can use a fold test or tracing to show a valid line of symmetry.
• I can draw a correct mirror line and complete the other half with matching corresponding parts.
• I can explain why a line is/is not a line of symmetry using clear evidence.