The use of a circle in this activity provides a wonderful tie-in to sixth grade geometry! Explain to the students how you came up with the dimensions of the sacred "black circle" using the length of the tallest member of the group. In math terminology, what term would we use for that length? (Hint: You can give them the definition, which is the distance from any point on the circle to its center.) That's right, that term is the "radius!"

Now, how could we use the radius (given to us by the height of the tallest person) to figure out how big to make the circle (AKA its circumference)? We would use the formula for the circumference of a circle. See if they can recall the formula on their own first. It is circumference = 2(pi)r, where pi = 3.14159 (or thereabouts) and r = the radius.

Have the students do some basic multiplication to figure out the circumference of the circle based on the tallest student's height. Then, compare this to the actual circumference of the circle (do this by simply measuring the length of the tape marking out the circle on the ground). Were they the same? Or maybe slightly off?

Now, divide the students into two groups. Group "A" will pick a student, determine their height, and figure out the circumference of the circle based on their height being "r." The other group would take the same height "r" and actually make the circle on the grass, without calculating the circumference. Then the two groups would compare the results. If time allows, have the students switch and try with another height "r."
 

This extension supports the mathematics concepts of measurement and geometry. (Click for a quick review of Math Grade 6, Measurement and Geometry-Standards 1.1 and 1.2.)