In a former life, I was an elementary school teacher. One the last day of school I would spray each child's desk with shaving cream and let them play around a bit before using a paper towel to wipe it all away. It was fun for the kids and it was a great way to have them clean the desks. It really did take off all the old pencil marks and made the desks look new.
I had forgotten all about this, until a friend mentioned that she does the same thing with her kids at home.
This is a great activity for a wide range of ages. I had mine do it on our patio table outside so that we could just spray it off when they were done. They made a HUGE mess, but I think they would have been ok doing it inside with a little direction about keeping it on the table!