CCSS.Math.Content.3.G.A
The standard
Reason with shapes and their attributes.
Common Core State Standards for Mathematics
What this standard means
Students need to describe shapes by their features, not by how they look on the page. They should name sides, angles, parallel lines, and right angles, then use those features to sort shapes into groups. They also need to see that a shape can belong to more than one group, like a square being a rectangle and a rhombus.
Mastery looks like clear reasoning: “I know this is a quadrilateral because it has four sides.” Students often get stuck on tilted shapes, skinny shapes, or mixed categories. They may think only a “regular-looking” example counts, so use many examples and non-examples.
Ways to teach it
- Give pairs a bag of cut-out polygons and have them sort by one rule, then trade bags and guess the rule.
- Ask students to write: “A square is also a rectangle because…” and support the claim with shape features.
- Show five shapes and ask students to circle all quadrilaterals, then explain one choice in one sentence.
- Have students find and sketch three quadrilaterals in the classroom, then label sides, corners, and any right angles.
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Related standards
- CCSS.Math.Content.2.G.A
Reason with shapes and their attributes.
- CCSS.Math.Content.2.G.A.1
Recognize and draw shapes having specified attributes, such as a given number of angles or a given number of equal faces. Identify triangles, quadrilaterals, pe...
- CCSS.Math.Content.1.G.A.1
Distinguish between defining attributes (e.g., triangles are closed and three-sided) versus non-defining attributes (e.g., color, orientation, overall size); bu...
- CCSS.Math.Content.1.G.A
Reason with shapes and their attributes.