Mix up some plain sugar cookie dough, or buy a tube of sugar cookie dough from the store*. If you make your own, add a couple of drops of green food coloring to the batter while it's still in a creamy state, before you add all the flour and it gets clumpy.
Nice bilateral hand use and good downward pressure to keep the mat from sliding around the table.
Our cookies ended up to be only about 1/8" thick, so they burned in the 350 F oven after only about 10 minutes. Hope yours end up just a little brown around the edges and chewy in the middle.
*Update: I'm having second thoughts about using dough with fresh eggs--my students don't always wash their hands very well and I sure don't want them to get sick from anything we use. What do you think?