A DGS like CABRI offers a good chance to explore geometrical properties working on given figures.

If you have CABRI II plus, you can use these materials:

Without CABRI, you can use these CabriJava files:

But CABRI is also an environment where pupils have the chance of coming across mathematical concepts working freely on their own projects. The problem is that pupils spontaneously use CABRI as a graphic tool. If they are asked to build a determinate polygon, for example, they connect segments by eye and don't think about the geometrical properties.

Pupils should understand that the perception often leads to wrong deductions. For example, a square is always a "true" square?
They were invited to explore with Cabri if a given square was "dragging resistant" and to find out if it was a "true" square by measuring lengths and angles and/or by verifying if two sides were perpendicular or parallel.

Cabri file | CabriJava

An other task was to produce themselves drawings dragging resistant. This is a complex operation, because it involves drawing circles, lines and segments, then hiding the parts you won't to see in the final picture.
The figures built in this way were saved as "macro" and used later . to construct more complex drawings by building reflections, symmetries and traslations.