During measurement topic, ask the students, how can a shape be both bigger AND smaller than another. For example, I used this doing perimeter and area of a semi-circle. I drew two diagrams on the board with particular dimensions where one with the smaller perimeter had a larger area. It would work with many different ones though and could be used for example to show how the largest area for a ‘rectangle’ is when the sides are the same (ie. a square). On this last one, there was a good site I came across for exploring this – complete with video and an image I turned into a worksheet (Perimeter v Area). Also later discovered this resource looking at which shapes have the greatest area (with links to further resources!)