This activity is good for introducing pupils to the exploration of spatial mathematics. It allows the pupils some degree of freedom as to how they approach it and record their findings.

Using something bigger than dominoes like giant lego (or just large dominoes) and initially introducing the challenge altogether will help learners 'get into' the problem. Pupils can then be left to find other rectangles, perhaps in pairs.

If you have an interactive whiteboard, you may find our Dominoes Environment useful for this problem.

Tell me about the differences between this one and that one. (Having chosen two that have the same outline.)

Are there any other ways you could put those dominoes together to make a rectangle?

Allow the pupils to ask "I wonder what would happen if we ...?". For example they could place a domino on its edge.

Having access to dominoes, or as many congruent cuboids as possible, will help.