Unit Plan 24 (Grade 3 Math): Shapes & Attributes—Triangles, Quadrilaterals, Polygons
Classify polygons by shared attributes; build quadrilateral family trees; justify with properties and counterexamples (e.g., all squares are rectangles).
Focus: Classify by shared attributes; use categories/subcategories (e.g., all squares are rectangles) and justify with properties.
Grade Level: 3
Subject Area: Mathematics (Geometry • Reasoning about Structure)
Total Unit Duration: 5 sessions (one week), 45–60 minutes per session
I. Introduction
Students sort and classify polygons by their attributes (side lengths, angle types, parallel/perpendicular lines). They build a “family tree” of quadrilaterals, learn that categories nest (a square is a rectangle and a rhombus), and practice giving counterexamples to test claims.
Essential Questions
- Which attributes define a shape category, and which are just appearance details?
- How do categories and subcategories (e.g., quadrilateral → rectangle → square) relate?
- How can an always/sometimes/never statement be tested using counterexamples?
II. Objectives and Standards
Learning Objectives — Students will be able to:
- Identify and use defining attributes to classify triangles, quadrilaterals, and other polygons.
- Explain how shapes in different categories may share attributes, forming larger categories (e.g., all squares are rectangles).
- Draw examples/non-examples of shapes with specified properties (e.g., parallel sides, one right angle).
- Use structure (MP.7) to notice regularities and build rules for classification; apply regularity (MP.8) to justify claims.
- Communicate reasoning with precise vocabulary, labeled diagrams, and counterexamples.
Standards Alignment — CCSS Grade 3
- 3.G.1: Understand that shapes in different categories may share attributes; recognize that shared attributes define larger categories; identify/describe quadrilaterals (e.g., rhombuses, rectangles, squares); draw examples with specified attributes.
- MP.7: Look for and make use of structure.
- MP.8: Look for and express regularity in repeated reasoning.
- (Supporting) MP.6: Attend to precision (labels, units, diagrams).
Success Criteria — Student Language
- I can sort shapes by attributes and explain my rule.
- I can show that a square belongs to more than one category (it is a rectangle and a rhombus).
- I can draw a shape with specified properties and justify why it fits.
- I can test a rule with a counterexample and revise the rule if needed.