I had the students roll out their clay slab to be about 1/4" thick, having them lay their hand down next to it to make it about the same thickness as their finger as a way to measure. Then they traced around a circle stencil or paper plate to cut out their circle.
They created their symmetrical designs first on paper and then on the clay by incising into the clay and also building onto the clay to create a textural piece.
We used metallic acrylic and tempera paints on top of the air-dry clay.
FYI- I did this project during a summer class that did not have as many students as my public school classes but it would be very do-able in school. My students were grades 2-4. They came out beautiful!