The learner classifies familiar plane shapes according to observable attributes such as number of sides or vertices, whether sides are straight or curved, and whether a shape has equal-length sides, while distinguishing defining properties from non-defining features such as color, size, or orientation. A shape may fit different categories under different rules, and recognizing these relationships supports precise geometric description and later classification; formal angle measurement, symmetry, and advanced shape hierarchies are not included.
To sort shapes, look for a rule about what the shapes are like. Use features such as:
Do not use color, size, or how the shape is turned. These features can change without changing the shape.
Example: Sort these shape cards by the number of straight sides:
Step 1: Look at one shape at a time.
Trace the outside of the shape with your finger. Count only the straight sides.
Step 2: Count the sides.
| Shape | Straight sides |
|---|---|
| Triangle | |
| Square | |
| Rectangle | |
| Circle |
The circle has a curved boundary, so it has no straight sides.
Step 3: Put shapes with the same number together.
The square and rectangle belong in the same group for this rule, even though they look different. The colors, sizes, and the rectangle’s position do not change the number of sides.
Always check the sorting rule first. A shape might belong to a different group if you use a different rule, such as “has curved sides” or “has corners.”
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