The reason to reason

By Ian Davies
Published 24 February 2022

Ian talks about empowering students to draw their own mathematical conclusions through conversation.

It’s important to have great maths conversations because they guide students to use precise mathematical language in their reasoning.

Me: The question says ‘Give a reason for your answer’. What reason would you give?

Student: 64 add 73 is 137, 180 subtract 137 is 43.

Me: Is that a reason or a series of calculations?

Student: Err…it’s why the answer is 43.

Me: It’s how you get the answer 43 from the numbers in the question. For the reason, I need to know why you did those calculations.

Student: Because it’s a triangle.

Me: Tell me more – what about a triangle? Is it because the triangle has got three sides?

Student: No it’s because they add up to 180.

Me: We’re getting there! What adds up to 180?

Student’: The angles.

Me: What angles? We’re very nearly there now!

Student: The angles in the triangle add up to 180 degrees.

Me: Perfect – that’s the mathematical reason – ‘The angles in a triangle add up to 180 degrees’.

When we think of maths, we tend to think of numbers and how we can manipulate them, using logical methods to find definitive solutions. But maths is more than numbers: we need to ensure that we’re providing students with the opportunity to develop precise mathematical language to justify the numbers, methods and calculations they use.

The conversation above was between me and a Year 11 after a mock exam where many students had lost marks in questions that said ‘Give a reason for your answer’. Questions like these, that ask students to ‘Describe’ or ‘Explain’, can stump students who are able to reach the correct numerical answers, but often struggle with (or, in some cases, completely ignore) the requirement to give mathematical justifications for their method and solution. Without this reasoning, the student’s depth of understanding is unclear.

Reasoning skills can be developed in other areas of the maths curriculum, such as transformations for example. I like to challenge pupils to work in pairs to precisely describe transformations, asking questions like “how much information do you need?” and “would someone be able to perform the transformation given the information you’ve written down so far?”. Asking students to verbally criticise each other’s answers gives them the practise they need in using mathematical language precisely before they write their own descriptions down.

Mathematical reasoning shows that students haven’t just stumbled upon the answer or learnt a method by rote, it demonstrates they have a deeper understanding and a solid grasp of mathematical concepts that can be applied to increasingly complex problems. As teachers, we need to guide students through conversation and tease out what detail is needed to answer a question.

These conversations promote the use of precise mathematical language to convey methods accurately and, rather than giving a set of stock phrases to learn, empower students to draw their own mathematical conclusions and increase the possibility of them making new, meaningful contributions to mathematics in their futures.

First published July 2021.

Author

Ian Davies

Ian Davies

About the author

Ian has worked in mathematics education for over thirty years and is Head of Curriculum for White Rose Maths.

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