Perimeter Patrol

Teacher Facilitation Guide | Tier 2 Intervention

Standards Focus

CO 3.MD.D.8

Learning Objective

Students will define perimeter as the distance around a shape and distinguish it from area (the space inside). Students will build rectangles with the same perimeter but different areas using physical manipulatives.

Materials Needed

Linking Cubes (at least 24 per student)
"Around the Edge" Worksheets
"Cube Construction Mat" (laminated)
Dry erase markers
Highlighters (Yellow and Blue)

1. The Boundary Hook (5 mins)

Goal: Connect perimeter to the physical concept of a fence or boundary.

Ask: "If we wanted to build a fence around a backyard to keep a puppy in, would we put the fence under the grass or around the edges?" Use a linking cube to demonstrate "walking" around the edge of a book or desk.

2. Explicit Instruction: Around vs. Inside (10 mins)

Modeling with Cubes:

Area: Fill a $2 \times 3$ rectangle with cubes. "The 6 cubes we used to fill the space is the Area. It's what is inside."
Perimeter: Trace your finger around the outside edges of the cubes. "The total length of these outer edges is the Perimeter. It's the boundary."
Action: Have students use a blue highlighter to color the perimeter of a drawn rectangle and a yellow highlighter to fill the area.

3. Guided Construction (15 mins)

Guide students to build a rectangle that is 4 units long and 2 units wide.

Count the total cubes (Area = 8 sq units).
Count the unit segments around the outside (Perimeter = 12 units).
Common Misconception: Students often forget to count the corner segments twice (once for each side). Use the "finger-step" method to ensure every segment is touched.

4. The Perimeter Challenge (15 mins)

Challenge students to see if they can build DIFFERENT rectangles that all have a Perimeter of 12 units.

Option A: $5 \times 1$ Rectangle

Perimeter: $5+1+5+1 = 12$
Area: $5$ square units

Option B: $4 \times 2$ Rectangle

Perimeter: $4+2+4+2 = 12$
Area: $8$ square units

Option C: $3 \times 3$ Square

Perimeter: $3+3+3+3 = 12$
Area: $9$ square units

Discussion Question: "If the distance around stays the same, why does the amount of space inside change?"

Progress Monitoring Look-Fors

Skill	Proficient Indicator
Terminology	Uses "Perimeter" for the edge and "Area" for the tiles inside correctly.
Measurement Accuracy	Counts every unit segment around the edge, including corners, without skipping.
Problem Solving	Can create at least two different shapes for a given perimeter length.
Independence	Differentiates between adding side lengths (perimeter) and multiplying/counting tiles (area).

Scaffolding Strategies

1
Tactile Trace: Use textured yarn or pipe cleaners to wrap around the cubes to literally "feel" the perimeter.
2
Color Coding: Always use Blue for perimeter and Yellow for area in drawings to create a consistent visual anchor.
3
Sentence Frames: "The Area is ______ squares because it is inside. The Perimeter is ______ units because it is around."

Perimeter Patrol

Perimeter Patrol Teacher Guide

Around the Edge Worksheet

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