Estimate the lengths of these lines in centimetres.

Add your estimates together.

Hint: Your classroom door is probably two metres tall. How do the lines compare to that length?

A Mathematics Lesson Starter Of The Day


Topics: Starter | Estimating

  • Marilyn Heath, 182736
  • Brill starter for Y6 lesson on estimates & approximation.
  • Transum,
  • The guess is that in the typical Mathematics lesson there are not as many opportunities for estimation as there should be. Whether it is estimating lengths, angles, weights or time the techniques for arriving at a good answer need to be practised. Do students know that the height of the classroom door is roughly two metres and can they use this as a comparison to estimate other lengths. A 1kg bag of sugar or flour is also a good resource to have in the classroom being a familiar weight to compare other weights with. Estimating answers to mathematical questions before accurately working out the exact answer is a very important check.

    Sorry, there are no answers for this starter because it depends on the size of your projected image. Perhaps when everyone has had chance to make their estimates, some students could come up to the board and measure the actual lengths of the lines.
    Teaching points could include:
    - Appropriate units of measurement to use;
    - Appropriate degree of accuracy
    Of course there is always the issue of correctly adding together the estimated lengths too!"

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The answer will vary depending on how large your projector image is. Use a tape measure or ruler to measure the lines then add the results together. Who in the class got closest to the sum of your measurements?

Note to teacher: Doing this activity once with a class helps students develop strategies. It is only when they do this activity a second time that they will have the opportunity to practise those strategies. That is when the learning is consolidated. Click the button above to regenerate another version of this starter from random numbers.

Teaching idea: Allow the pupils to work on this activity without any help. Once they have arrived at an answer, collect ideas from the class about strategies used then give the pupils a chance to re-estimate the lengths. As a point of reference, the classroom door is probably around 2m tall. Use a large ruler to find the correct lengths but stress that getting the answer exactly right was not expected.

Presentation Tip: Press the F11 key (except on MS Edge) to hide the tool bars if the lines don't fit on to your screen. You can also use the zoom option in your browser's menu to vary the display size.

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Laptops In Lessons

Teacher, do your students have access to computers?
Do they have iPads or Laptops in Lessons?

Whether your students each have a TabletPC, a Surface or a Mac, this activity lends itself to eLearning (Engaged Learning).

Laptops In Lessons

Here a concise URL for a version of this page without the comments.

Here is the URL which will take them to a related student activity.

Student Activity


Extension Activity

How many tins of paint are required to paint the Dome Café? Make some assumptions, do some research then estimate.

Dome Cafe

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