Foundations of Mathematical Thinking · Senior Infants

Active learning ideas

Perimeter of 2D Shapes

Hands-on activities work well for perimeter because young learners need to feel the boundary of shapes rather than just see static lines. Using everyday objects like blocks or string turns an abstract concept into something they can physically measure and discuss with peers, building confidence and accuracy.

• NCCA Curriculum Specifications
• NCCA: Junior Cycle - Measurement - M.1

• 25–45 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Experiential Learning
• 30 min · Pairs

Block Building: Perimeter Paths

Provide multilink cubes for pairs to build rectangles and squares on mats. Children measure each side by lining up cubes, record the number per side, then add for total perimeter. Compare perimeters of different shapes they create.

Which pencil is longer , can you show me?

Facilitation Tip

During Block Building: Perimeter Paths, encourage students to verbalize their measurements as they count cubes along each side to reinforce the idea of continuous measurement.

What to look for

Provide students with pre-cut squares and rectangles made from cardstock. Ask them to use unifix cubes to measure each side and then add the cube counts together to find the perimeter. Observe if they measure all sides and sum them correctly.

• Apply
• Analyze
• Evaluate
• Self-Awareness
• Self-Management
• Social Awareness

Activity 02

• Experiential Learning
• 45 min · Small Groups

String Outline: Classroom Shapes

Cut yarn into lengths for small groups to outline pre-drawn shapes on the floor, like rectangles and L-shapes. Stretch string along each side, measure with cubes, and calculate perimeter. Discuss why composite shapes have longer paths.

Can you put these sticks in order from shortest to longest?

Facilitation Tip

While guiding String Outline: Classroom Shapes, stand back and let groups troubleshoot their own string lengths before intervening to promote problem-solving skills.

What to look for

Give each student a drawing of a simple composite shape (e.g., an L-shape). Ask them to trace the perimeter with their finger and then write down how many unit cubes it would take to trace the outside edge. They can draw the cubes if needed.

• Apply
• Analyze
• Evaluate
• Self-Awareness
• Self-Management
• Social Awareness

Activity 03

• Experiential Learning
• 35 min · Whole Class

Perimeter Hunt: Shape Scavenger

Give whole class cards with shape outlines. Students find classroom objects matching shapes, use paper strips to measure perimeters, and share findings on a class chart. Extend to composite shapes like tables.

How many cubes long is this book?

Facilitation Tip

For Perimeter Hunt: Shape Scavenger, provide clipboards and pencils so students can record their findings and compare results with classmates afterward.

What to look for

Show students two different shapes, one larger square and one smaller rectangle. Ask: 'Which shape has a bigger perimeter? How do you know?' Encourage them to explain their reasoning using their measuring tools or by counting sides.

• Apply
• Analyze
• Evaluate
• Self-Awareness
• Self-Management
• Social Awareness

Activity 04

• Experiential Learning
• 25 min · Individual

Playdough Perimeters: Custom Designs

Individuals roll playdough into sides of rectangles or squares. Measure each side with links, compute perimeter, then join shapes into composites and re-measure outer path only.

Which pencil is longer , can you show me?

Facilitation Tip

When introducing Playdough Perimeters: Custom Designs, model how to press the playdough into a flat shape and trace the edge with a ruler to maintain focus on the boundary.

What to look for

Provide students with pre-cut squares and rectangles made from cardstock. Ask them to use unifix cubes to measure each side and then add the cube counts together to find the perimeter. Observe if they measure all sides and sum them correctly.

• Apply
• Analyze
• Evaluate
• Self-Awareness
• Self-Management
• Social Awareness

A few notes on teaching this unit

Teachers should always model measurement techniques using the same materials students will use, such as counting cubes aloud or stretching string tightly around a shape. Avoid pre-teaching formal rules; instead, let students discover that squares and rectangles follow the same addition rule by comparing their own measurements. Group work helps students articulate their thinking and correct each other’s misunderstandings in real time.

By the end of these activities, students will measure each side of a shape, add the lengths together, and explain why the total distance around the outside is called the perimeter. They will also begin to recognize that different shapes can have the same perimeter depending on their side lengths.

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Watch Out for These Misconceptions

• During Block Building: Perimeter Paths, watch for students filling the inside of the shape with cubes instead of tracing the edges.

  Ask them to remove the cubes from the inside and focus only on the outer layer, then recount the cubes to reinforce the boundary concept.

• During String Outline: Classroom Shapes, watch for students measuring the string while it is still wrapped around the shape.

  Have them straighten the string first, then measure it against a ruler to emphasize the linear distance of the perimeter.

• During Perimeter Hunt: Shape Scavenger, watch for students assuming all sides of a composite shape contribute equally.

  Prompt them to build the shape with blocks first, then trace only the outer edges with their fingers to identify shared sides.

• During Playdough Perimeters: Custom Designs, watch for students treating squares as having a different perimeter rule than rectangles.

  Provide a square and rectangle side-by-side with the same side length, then have students measure both to see that adding all sides applies to both.

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Methods used in this brief

• Experiential Learning