In place value, children learn about the value of each digit in a number (e.g. that the 5 in 153 represents 5 tens) – the Deepening Understanding in Column Value blog gives some ideas for extending thinking in these lessons. However, to give children a more complete understanding it’s important that they can also reason about the relative size of numbers. In this blog I will explore how I’ve used a blank number line to develop this form of understanding and look at the wealth of opportunities for reasoning that it can provide.

Consider this task. Children are given a long number line with 0 and 100 at either end and are asked to position 31, 39 and 84 accurately on the number line. Children are challenged to think about whether the lengths between the numbers are appropriately sized.

I have found that children are generally able to order numbers, but that the common mistake is to make the spaces between numbers too similar. In this example, I may ask children to compare the distance between 31 & 39 with the distance between 0 & 31 (which is almost four times longer) and the distance between 84 & 100 (which is exactly twice as long).

In a similar task, children have positioned 4, 7 and 9 on a 0-10 number line. It’s common for children to position 4 by counting four small ‘steps’ on from zero (placing 4 far too close to zero) rather than thinking about the position of 4 relative to the half-way point of the line. Similarly, 7 and 9 are often positioned by counting back from 10, leaving an overly large gap between 4 and 7. With careful modelling, and by looking at the number lines in the classroom, children learn to reason spatially with greater precision.

I’ve included two such tasks in I See Problem-Solving – LKS2 (click on the link for sample tasks), which is due to be released on 29th September. Here’s one of the pages from the Worked Example:

And here is the extension prompt for the task. There’s so much additive and multiplicative reasoning that go into estimating the value of the missing numbers:

I would love to hear about any practical examples of how you are outworked these ideas in the classroom. The blog Deepening Understanding of Column Value gives some more ideas for how to deepen the challenge in place value. Have a great term!

For information about NCETM-accredited training by Gareth Metcalfe, please visit – bookings are being taken from Spring term 2020 onwards.

2 thoughts on “Place Value: Seeing the Relative Size of Numbers

  1. Thank you for releasing this just as we are about to start our White Rose Place Value blocks. I have forwarded it to all the KS1 and 2 teachers at our school and know they will find it helpful.

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