When we are in the Southwest region of our Native American unit, I take the kids outside (while the weather is still nice!) and we grind corn to get a feel for what it would have been like. Last year, I didn't do it with my class since it was a new social studies curriculum in my new district, but I missed the activity and wanted to do it this year with my class.
One rock per student, fist size or larger
One tub per group to hold materials (I use a plastic dish pan - $1.98 each)
Ears of squirrel corn, two or three per group
Cup and/or Ziploc to hold ground corn, one per group
I assemble students into groups of four and give each group a tub with the following materials - one rock per student, two to three ears of corn, a cup and a sandwich-sized Ziploc bag. We go outside and choose a square on the sidewalk for each group. I do not offer any advice or tips. I let them figure out techniques and such on their own. I give them about a half-hour, and they need to get the ground corn into the cup/Ziploc. Then we come inside (after stopping by the restroom to wash up) and discuss things like if we would like this for a daily job, if it was harder/easier than expected, what techniques were successful, etc.
It's a very memorable day and the kids just love it!