When I taught 6th grade math I would have students inscribe a circle within a square and draw perpendicular diameters that thus created 4 “radius squares”. They had already discovered pi in previous lessons (but I would not remind them). Then I would ask them to write down a secret estimate of how many “radius squares” rounded to the nearest tenth they would need to cut up like Mosaic chips to fill in the area of the circle. Then I had them duplicate the squares and complete the Mosaic.
Lessons learned: Pi will pop up often, even if you aren’t expecting it to show itself. Also the quick way to estimate the area of a circle is to find the area of a square made from the radius and then multiply that by 3.