Greek Discus Project for Kids
To make a pretend discus like this one, not to throw but just to display, carve it out of styrofoam or clay, and then paint it with gray or brown paint. If you want to try holding a competition to throw a real discus, you can buy discuses at sports stores. If you want to hold your own Olympic Games and you don't want it to be too complicated, you can use a Frisbee instead of a discus.
For more ideas for Ancient Greek projects, check out these books from Amazon or your library:
Ancient Greece!: 40 Hands-On Activities to Experience This Wondrous Age (Kaleidoscope Kids), by Avery Hart, Paul Mantell, and Michael P. Kline (1999). Gives ideas to get kids thinking, rather than step-by-step instructions.