Classifying polygons

Most classrooms have a poster of shapes. Often there is only one example of each shape, with a 'standard' appearance.

• The triangle is usually acute-angled with a horizontal base.
• The quadrilaterals, other than kites, usually have one or two horizontal sides and therefore some of them also have vertical sides.
• The trapezium usually has two (or three) equal sides with the longer side on the base and a shorter side above it.
• The rectangle usually has the longer side on the base.
• The pentagon is usually regular, with one side horizontal.
• The hexagon is usually regular, with a pair of sides horizontal or vertical.
• All the shapes are convex.

Pattern blocks, which are used frequently in primary classrooms, reinforce this standard perception.

What shape is a baseball 'diamond'? It is a square.

What shape is this?

A trapezium.

You can download the Naming Polygons: Information Sheet, Regular and Irregular Polygons: Information Sheet and the Convex and Non-convex Polygons: Information Sheet which provide more varied examples.