# 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.

## 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.