Mathematics · Foundation · Comparing Length: Longer and Shorter · Term 2

Using Informal Units to Measure Length

Students calculate the perimeter of various polygons, including irregular shapes, using appropriate units.

• ACARA Content Descriptions
• AC9M6M01

About This Topic

Using informal units to measure length helps Foundation students grasp measurement by lining up everyday objects like blocks, hands, or paperclips along lines and shapes. They practice iterating units without gaps or overlaps to find the perimeter of polygons, including irregular ones cut from paper. This builds spatial reasoning as students trace outlines, cover edges completely, and record counts, answering questions like 'How many blocks long is this book?' or 'Can you measure the table using your hands?'

Within the Australian Curriculum, this topic develops early number sense and geometry understanding, linking to AC9M6M01 standards on measurement processes. Students discover that different unit sizes yield varying counts for the same length, prompting reflection on consistency and reliability. These experiences lay groundwork for formal units and precise tools in later years.

Active learning shines in this topic because students handle physical units, feel the impact of overlaps or gaps, and compare results with peers. Collaborative measuring tasks reveal patterns in data, while discussions clarify why uniform units matter, making measurement intuitive and engaging.

Key Questions

1. How many blocks long is this book?
2. Can you measure the table using your hands?
3. Why might we get a different answer if we use different-sized objects to measure?

Learning Objectives

• Compare the lengths of different objects using informal units.
• Measure the perimeter of simple polygons by counting informal units.
• Explain why using different informal units results in different measurement counts.
• Demonstrate how to measure a length without gaps or overlaps.

Before You Start

Comparing Objects by Length

Why: Students need to be able to identify which objects are longer or shorter before they can measure length.

Counting to 20

Why: Students must be able to count the informal units accurately to determine the measurement.

Key Vocabulary

Length	The measurement of how long an object is from one end to the other.
Perimeter	The total distance around the outside edge of a shape.
Informal Unit	A non-standard object used for measuring, such as blocks, hands, or paperclips.
Measure	To find out the size or amount of something, like length, using a unit.

Watch Out for These Misconceptions

Common Misconception

Larger units always give larger numbers.

What to Teach Instead

Students think bigger units mean more counts, but activity swaps show fewer large units fit. Peer sharing of measurements corrects this, as groups compare side-by-side results and discuss coverage efficiency.

Common Misconception

Units can overlap or leave gaps.

What to Teach Instead

Overlaps shorten apparent length; gaps lengthen it. Hands-on lining tasks let students self-correct through trial, with teacher prompts during rotations reinforcing straight, snug placement.

Common Misconception

Perimeter is the same as the area inside.

What to Teach Instead

Students confuse edge length with enclosed space. Tracing and unit-covering activities distinguish boundaries from interiors, as pairs verbalize 'around the edge only' during group checks.

Active Learning Ideas

Partner Chain: Measuring Books

Pairs select classroom books and measure perimeter using linking cubes laid end-to-end. They count units for each side, add totals, then switch units like hands for comparison. Record findings on charts and discuss differences.

25 min·Pairs

Shape Hunt: Perimeter Paths

In small groups, students find polygons like windows or drawings, trace outlines on paper, and cover with straws or fingers. Count units per side and total perimeter. Share results, noting irregular shapes.

35 min·Small Groups

Unit Swap Challenge: Whole Class

Display a long rope; class measures perimeter using blocks first, records count, then repeats with larger units like feet. Tally results on board and graph comparisons to spot patterns.

40 min·Whole Class

Build and Measure: Individual Mats

Each student builds irregular polygons with toothpicks on mats, then measures perimeter using beads. Adjust for full coverage, recount, and label drawings with unit counts.

20 min·Individual

Real-World Connections

• Construction workers use non-standard objects like their own hands or feet to quickly estimate lengths on a building site before using formal tools.
• Parents might use toys like building blocks to measure the length of a child's bed or a rug to see if it fits a specific space in their home.

Assessment Ideas

Quick Check

Provide students with a pencil and a set of 10 identical blocks. Ask them to measure the length of their desk using the blocks. Observe if they place the blocks end-to-end without gaps or overlaps and ask: 'How many blocks long is your desk?'

Exit Ticket

Give students a drawing of a simple rectangle and a strip of paper. Ask them to trace the perimeter of the rectangle with the paper strip and then cut the strip to match the perimeter. Finally, ask them to count how many paper strips long the perimeter is.

Discussion Prompt

Ask students: 'Imagine you measured your book using large blocks, and your friend measured the same book using small buttons. Whose measurement would have more items? Why?' Listen for explanations about the size of the unit affecting the count.

Frequently Asked Questions

How do informal units build measurement skills in Foundation math?

Informal units like blocks or hands let students experience iteration and addition before abstract numbers. By measuring familiar objects, they connect counting to real-world lengths, understand unit consistency matters, and develop spatial language. This aligns with ACARA goals, preparing for formal metrics through playful, tangible practice that boosts confidence and accuracy over time.

What activities teach perimeter with informal units?

Try partner measuring of books with cubes, shape hunts tracing classroom polygons with straws, or class challenges swapping unit sizes on ropes. These 20-40 minute tasks use everyday materials, encourage recording and comparison, and address key questions like why units affect counts. Students build polygons themselves for deeper ownership.

How can active learning benefit teaching informal measurement?

Active learning engages Foundation students kinesthetically: they manipulate units, negotiate placements in pairs, and debate results in groups. This uncovers misconceptions like gaps instantly, as peers spot errors. Collaborative data graphing reveals unit size impacts, fostering discussion and retention far beyond worksheets, while movement keeps energy high.

Why do different units give different answers for length?

Unit size determines count: small blocks fit more along a line than large hands. Foundation activities swapping units on tables or shapes demonstrate this empirically. Students tally and compare class data, realizing consistent, identical units ensure fair measures, a concept vital for curriculum progression to rulers and meters.