Now that I finally have some time, I can upload some of the projects we did during the year. This particular one was done by my 5th/6th graders as a fill-the-time activity. Optical illusion projects are great for that. Simply draw a grid with 12 boxes. The students used templates, like milk jug caps, sour cream lids, and yogurt lids to make the circles. Each square had to have the smallest circle start in a different spot. The rings that radiated from it just kept going until they ran into an edge. They used a black Sharpie to color it in.