This task develops learners' familiarity with Carroll and Venn diagrams in the slightly unusual context of geometry. It will encourage them to interrogate the data carefully and provides a 'reason to reason'.
This activity featured in an NRICH Primary webinar in March 2021.
Display the four shapes on the board and ask the class what they notice. Allow time for learners to think on their own before talking to a partner and then sharing ideas with the whole class (think-pair-share). As you take feedback, try to value everyone's contributions.
You may find that the idea of comparing and contrasting the shapes comes up naturally, and you can use this to lead into the first question. You might write up the different ways of sorting that the class suggest on the board.
At this point, it would be good not to say too much more. Give out the sheets of the six diagrams one between two and give some time for the class to look at each one without being explicit about the task at first. Encourage learners to share what they notice and any questions that they have with the whole class before explaining the task. (You may find that some pairs predict the task, or begin working on it before you spell it out but that does not matter at all!). If learners cut the sheet into six 'cards', they could physically put diagrams close together which might help.
In the plenary, you could invite several pairs to explain how they got started on the task, and how they worked through to their conclusion. Encourage appropriate use of geometrical vocabulary, and clear reasoning. You can ask pupils to say in their own words what they think another pair has said. This will help everyone follow the reasoning and feel empowered to seek clarification where appropriate.
Tell me about this Venn/Carroll diagram. What does it show?
How will we find a Carroll/Venn diagram that matches it? What will we look for?
Why are these two shapes both in this region/cell? How might this help us find the matching Venn/Carroll diagram?
Having the diagrams on individual cards will make comparison easier for some pupils. Encourage learners to talk about what each diagram shows outloud with their partner.
You could challenge learners to create another matching pair of diagrams for these four shapes.