March 14 is Pi day! That is, 3/14, and the NES lesson, Calculator Controlled Robots, has a mission devoted to circles and Pi.
In mission 4, students create three different size circles using three different robot wheel movements. They can attach a marker at different positions as well as use different turn commands to create larger or smaller circles. For each circle, students measure the diameter with a length of string and determine how many string-lengths it takes to go around the outside of the circle.
This helps them discover that the distance around each circle, no matter what size is a little more than three lengths of string, or the diameter, for each circle of different diameter. The discovery of Pi leads to the circumference formula as well as the area formula.