Benchmarks for metres and centimetres (PDF, 35 KB)
*Measurement progression, 2nd–3rd steps *

## The purpose of the activity

In this activity the learners develop an understanding of the size of a metre and a centimetre by developing personal benchmarks for the two measures. The learners also develop their skill at estimating the length of objects in metres and centimetres.

## The teaching points

- The learners will understand the need for having and using standard measures of length (metres and centimetres).
- External benchmarks (for example, visualising three 30-centimetre ruler lengths for 1 metre) can be used to conduct estimation tasks.
- The learners will be able to measure using rulers. (This includes the use of zero as the start point for taking a measurement or, if the ruler is ‘broken’, knowing the length measure is the difference between the start point and the end point.)
- Discuss with the learners the situations where it is important to know how long a metre and centimetre is.

## Resources

- Metre length strips of paper or masking tape.
- Metre rulers.
- Centimetre cubes or centimetre squares.
- A selection of everyday objects under 10 centimetres in length.

## The guided teaching and learning sequence

1. Begin the session by showing the learners a metre-long strip of paper or a metre length of masking tape stuck to the floor. Ask:

“How long do think this strip of paper/tape is?”

“Why do you think that?”

Challenge the learners to think about how they came up with their estimate.

2. Show the learners a metre measuring stick. Ask:

“Is the strip longer or shorter than a metre?”

3. Measure the strip of paper/tape using the metre stick/ruler to show that it is a metre. This is also an opportunity to ensure the learners appropriately use a metre ruler by lining up the start of the paper with the “0” mark on the ruler.

4. Next ask the learners to think about what they could do if they didn’t have access to measuring tape or a ruler for measuring an object in metres. This discussion should focus on the importance of students developing personal benchmarks for measuring lengths. Your questioning may need to be more specific by posing prompts such as “How could you use parts of your body to show 1 metre in length?”

5. Give each learner or group of learners a metre length of paper or string. Ask them to use this to find a metre length on their body that could be used as a personal benchmark.

6. Once the learners have shared a number of possible personal benchmarks for 1 metre (for example, the length from their wrist to their shoulder, etc.) have them try to use it to find as many objects in the room that are 1 metre long (for example, the length of two desk tops, the height of a computer table). Have them record the objects they find that they estimate to be 1 metre in length.

7. Discuss with the learners the reason for having standard measures such as metres.

The rest of this guided learning sequence repeats the above steps with a centimetre length. This could be taken as a separate teaching session.

8. Show the learners a centimetre cube or a centimetre square of paper. Ask the learners:

“How long do think a side of this cube or square is?”

“Why do you think that?”

9. Ask individual learners or pairs of learners to find objects that are 2 centimetres, 5 centimetres, and 8 centimetres in length.

“Why do you think that object is 2 centimetres? 5 centimetres? 8 centimetres long?”

Challenge the learners to think about how they came up with their estimate.

10. Ask the learners to compare their lengths with another learner’s or pair of learners’ lengths and jointly decide which objects are the closest estimates to the three lengths. 11. Give the learners a centimetre cube or centimetre square of paper and say:

“This is 1 centimetre in length. Do you think your estimate of the 5-centimetre-long object is too short, too long or about right?”

12. Get the learners to use the centimetre cube to measure the length of the 5-centimetre-long object. This is an opportunity to check that the learners are able to repeat the use of a single unit to measure length.

13. Ask the learners to think about what they could use as a personal benchmark for 1 centimetre. Your questioning may need to be more specific by posing prompts:

“How could you use parts of your body to show 1 centimetre in length?”

14. Once the learners have shared a number of possible personal benchmarks for 1 centimetre (for example, the width of a fingernail, half the width of a thumb) have them use it to ‘measure’ a number of objects.

## Follow-up activity

Ask the learners to cut strings of the following lengths using their personal benchmarks:

- 2 metres
- 9 centimetres
- 5 centimetres.

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