Why do this problem?
is good for allowing pupils to explore both shapes and number, or to choose a particular aspect to focus on. There is a lot of freedom involved and there are exciting things to find out. Learners will be able to take control of their own learning and choose their own direction in this task.
You could begin by showing some of the pictures in the problem on the screen for the pupils to see and talk about. What similarities do they notice? What differences? They may pick up on the fact that the common link is the number $28$ straight away, but if not you can ask questions to probe them further. If some would like more examples they can be found here.
You can then set the group off on their own ideas using the number $28$. Pupils should be encouraged to ask themselves questions like " I wonder what would happen if I ...?", making a small change and exploring further.
Tell me about what you've got here.
Is there anything special about this shape you have made?
Can you find another arrangement?
Talk about symmetry and look for final shapes that are symmetrical and those that are asymmetric.
There may be a need for help with those with less developed fine motor skills for moving the shapes and fitting them together. Magnetic shapes can sometimes help.