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What is a Carroll diagram?

What is a Carroll diagram?
We explain what a Carroll diagram is and how primary-school children are taught to use a Carroll diagram to sort data, such as a group of objects or numbers, methodically.
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What is a Carroll diagram?

A Carroll diagram is used to organise data and group it according to whether it fits certain criteria.

In Key Stage 1 children begin to be taught about sorting and teachers may ask a child to sort a group of objects into two groups according to a given criteria. For example: children may be given a box of shapes and asked to sort them into two groups: 'Shapes with curved sides' and 'Shapes with straight sides'. Alternatively, they may be given some number cards and asked to sort them into odd and even numbers.

Using Carroll diagrams to sort data

Carroll diagrams take sorting data a step further, asking children to sort objects or numbers into four boxes. Each box has to follow two criteria. For example:


Sometimes, Carroll diagrams involve numbers. For example, children may need to sort the numbers 8, 22, 18, 49 and 100 into the following Carroll diagram:

It is a good idea to encourage children to deal with one number at a time. For example: look at the number 8 and then go through each of the criteria in turn to work out which box it should go in, then cross off number 8 from the list. Next look at 22 and do the same, and so on.

In a similar way to Venn diagrams, Carroll diagrams encourage children to sort data methodically, but also provide good revision for properties of shapes and number facts.