*Walking the Plank*involves KS1 or KS2 children looking for properties that are the same and those that are different in an

*Odd One Out*task.

*Odd One Out*is a popular activity and particularly useful to assess understanding, perhaps during a plenary. You show any three objects -shapes, numbers, words or whatever - and ask the children to say which is the odd one out and, most importantly, why. It is their explanation of the 'how do you know?' question that encourages them to find a proof and shows their understanding.

It works well in a 'Pirates' context. Ask three children to come to the front of the class and stand in a row. They will need enough space to take three steps forward. Explain to the class that these pirates are going to walk the plank, but only one will drop off the plank into the water. The others will be saved and the class (the pirate crew) will decide which one will end up wet and which pirates will stay dry. Build it up as part of a story about life on a pirate ship to set the scene.

Give each of the pirates a card with either 3 numbers or 3 shapes - or anything else you would like to reinforce from your teaching.

The rest of the crew select one of the numbers as odd and explains why it is the odd one out in the set. If it is a good reason for being the odd one out, that pirate takes one step forward. If the class selects one pirate consecutively, then ask them to give a reason why one of the other pirates might be the odd one out.

Remember, what is obvious to a child may be different to the way we see something as the odd one out - accept all answers that are correct and can be proved. The numbers 8, 9 and 12 work well as an example. The odd one out could be:

**8...**

*it is not a multiple of 3... it is symmetrical... it looks the same upside-down... it is in the Fibonacci sequence... it is a cubed number*

**9...**

*it is not a multiple of 4... it is an odd number... it is a square number... it looks like a different number when upside-down... it has an odd number of factors*

**12...**

*it is a 2-digit number... it is not consecutive... it has no closed loops in it... it has a straight line...*

**Some thoughts on asking children to 'Prove it'.**

When you ask for reasons why they have chosen a particular number, encourage children to use practical resources and pictures to help support their explanation. It gives a very clear idea of their understanding.

For example, how can they prove that 9 is an odd number? They could use 9 counters or cubes and lay them in pairs until there is one left, or they may colour squares on a number track. How could they prove it is a square number? Perhaps with interlocking cubes arranged in squares.

To prove other statements, they can use digit cards to show that 12 has two digits, they can point to 8 and 9 on a number line to show they are consecutive and show that 12 is not consecutive to 8 or 9. They could hold a mirror vertically and horizontally across the 8 to prove it is symmetrical.

The important thing is that each of these methods is active and involves models or images to support their explanations.

**Related articles**

Pirates Maths Mystery

Problem solving cards to download and use

Making the most of the whole class maths starters