I put out a variety of items that make circles. This is a great activity to repurpose all kinds of items--plastic containers, cups, film canisters, PVC connectors, and marker lids. (You do save marker lids when you toss out dried markers, right?)
The kids experimented with painting circles.
A few kids made a some circles and moved on to other things. Others spent more time filling their papers or trying out different designs.
One boy worked at the table all alone...for a long time. He created circles and used a variety of sizes to fill in all the spaces. This is a guy that doesn't usually stay with an activity alone for so long. But he really seems focused on investigating the circles.
We talked about coins... at least I did. He listened but still continued to work. And worked some more after I stepped back and took pictures.
These activities--that allow kids to investigate the process--always seem to attract at least one kid for a long time. The child can decide how long to do something and when his work is complete. So--short or long--the investigation is just right for learning.