Mats.

Milo is just learning to work at the table next to Oscar. 

I found some great little carpet-type rugs, 18"x24", at Menards for two bucks each.  Bought six of them in a variety of colors.  Voila:  Montessori-style work mats!  The mats really do help the kids keep out of each others' space, and the soft pile keeps round things from rolling off the table.  Plus they work as sit-upons for the hardwood floor.  These are too stiff to roll up, and I want to store them flat, so for now they're just stacked on the floor in the schoolroom. 

But the buyers' remorse is already settling in:  I probably should have bought ten.