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2D Shapes and Perimeter
Introduction
Attributes of 2D Shapes
Using Attributes of 2D Shapes to Find Perimeter
Relating Perimeter and Area

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2D Shapes and PerimeterUsing Attributes of 2D Shapes to Find Perimeter

Tiempo de leer: ~10 min

In third grade, students are introduced to the idea of perimeter.

Progression of finding the perimeter:

(1) Students use concrete object (like paperclips) to build the boundary

(2) Students find the distance around the shape by counting the intervals or adding the number of units on each side.

Question
Answer

(3) Students use the geometric attributes of shapes to find perimeter more efficiently (by recognizing sides that are the same length and using multiplication).

Question
Answer

Try these activities by entering some correct and incorrect values, to see what students will experience. Click on each of the images below to try it:

When finding perimeter, there are complexities in understanding linear measurements on grids. Consider the following problem. Who is correct?

Three students were asked to find the perimeter of this square:

  • Tyler: perimeter is 12 units
  • Lexi: perimeter is 16 units
  • Maggie: perimeter is 8 units

The correct student is . Consider ways to illuminate these types of misconceptions with students: Drag the statements into the box for the correct student.

Counted 2 tick marks along the bottom of the square and multiplied that by 4.
Saw that 3 square units fit along each side. Therefore the perimeter of the entire square is 4 times that length.
Counted 4 tick marks along the bottom of the square, and multiplied that by 4.
Tyler (12 units)
Lexi (16 units)
Maggie (8 units)
Archie