Yes, it is a real gravitation shield! Well, not really, but it is a great thing to astonish people at first and then make them remember the electromagnetism they have been taught at school. It is also a great conversation and demonstration piece in a class studying electromagnetism.
Also, it can be done in five minutes if you find the materials.
It DOES nothing, but, to keep it short if a magnet moves near a conductive something it creates electric currents in it. In the tube they go around the circumference of the tube and create their own magnetic field, which repulses our magnet. And this makes it fall 4 times slower.
Step 1: Find the Tube
You need a longish (30 cm - 2 meters, it is perfectly your choice, about 1-3 cm inner diameter ) piece of conductive and non-ferromagnetic tube. Aluminium works well, but before buying it search the house, it is very likely that you'll find it somewhere. I cut a piece of the hanger rack from an old wardrobe.