Why do this problem?
is designed to encourage children to begin to visualise - in particular, to see an image in their head. There are two visualising aspects in this proble- imagining the act of adding a new cube, but also keeping in your head the picture of what is already there.
The activity will also help to familiarise your class with positional language (in front, behind, to the right of, to the left of, on top, underneath etc.).
Being able to visualise is a useful skill which children are often not used to drawing on. By explicitly talking about visualisation, and offering opportunities like this for your class to practise visualising, you will be encouraging children to use this skill in their independent problem solving.
To introduce the activity, you might like to give each child just two or three cubes. Ask them all to close their eyes and slowly describe an arrangement of these cubes to them, inviting them to picture what they hear in their heads. Then, give them time to make the "building" with their cubes and compare their models with their neighbour's.
You could also invite a child to imagine their own arrangement of cubes and describe it to the rest of the class.
The larger the number of cubes, the harder it might become for children to draw their own "buildings", so a digital camera might prove useful. In fact, drawing any number of cubes in 3D is rather tricky! If they are used to using it, isometric paper would help.
Can you see those two cubes in your head?
What about the third one?
If it is under/behind/ on the right of that one, where will it be?
As you picture each stage in your head, can you to draw it so that you can keep track of where the cubes are?
Tell me about the building in your head.
Learners could go on to More Building with Cubes
If children are completely lost suggest using the cubes to do this activity, Chairs and Tables