Are the following statements always true, sometimes true or never true?
How do you know?
Can you find examples or counterexamples for each one?
For the 'sometimes' cards can you explain when they are true? Or rewrite them so that they are always true or never true?
A hexagon has six equal length sides

Triangles have a line of symmetry

Squares have two diagonals that

Cutting a corner off a square makes a pentagon 
The base of a pyramid is a square

A cuboid has two square faces 
What about these more complex statements?
When you cut off a piece from

Triangles tessellate

The number of lines of symmetry

Quadrilaterals can be cut into two equal triangles 
You could cut out the cards from this sheet (word, pdf) and arrange them in this grid. Alternatively, you could use these interactivities to organise your
thinking: