ABSTRACT
The 3-D shapes which are likely to be encountered by primary children exhibit a particular rule between the number of vertices, edges and faces. The term 'cuboid' covers a particular class of prisms where the polygonal cross-section is a rectangle. A cylinder does not quite fit the prism definition, but could be seen as a limiting case in a series of prisms involving polygon faces with increasing numbers of sides. The pyramids which primary children normally encounter are 'right' pyramids — that is, their points are vertically in line with the centres of their polygon bases. Intuitively, planes of symmetry may be thought of as ways in which 3-D objects may be sliced to leave two identical 'halves', such that one half is the reflection of the other. Pyramids need not possess any planes of symmetry, although the examples encountered by primary children normally do.
