Treat Nature by the sphere, the cylinder and the cone. - Cézanne
When a student is having a difficult time understanding geometry, it is eye opening to walk outside and see the world.
Go outside with a notebook and pencil. Draw what you see - it could be the street, a building, your living room window, the roof of your house.... The list is endless.
Now ask your student, "what do you see?" Guide her or him toward seeing that the everyday things we encounter are geometric shapes. The street could be a rectangle or a line. A building may be a cube, or its facade a rectangle. Your living room window is perhaps a square. The roof of your house may be a triangle from the side. Gaze at the full moon and see a spherical object that looks like a circle.
Look inside your home, too. A soup can is a cylinder. Ice cream cones are aptly named!
The lesson from Cézanne is that our world, nature, the things we build, are all shapes to be discovered.