Label the shapes with their names and attributes.
Make labels for the shapes e.g. 4 sides, red. Pupils can use the labels given and also type in their own descriptions. Next, decide on criteria and sort them into groups. Ask pupils 'will all of the shapes fit into your groups? Tell me which ones will have to be left out.' 'Choose yellow for one group and a shape for the other... will any shape fit into both groups? Where would you put it?'