I began the class with everyone following as I drew the 8 head sized circles on the whiteboard, one above the other to show how the body's torso, waist, hips, legs, knees and elbows were proportioned. Then when we had established this in their sketchbooks for future reference, I had them make an picture of a person or persons on a blue cardstock by ripping the shapes out of colored construction paper. This way they could measure with the head size as they created their people in their artwork.
Actually, they kind of forgot about measuring and just went to town ripping and gluing making their masterpieces. It was fun to watch them get lost in the process, accessing their right brains and going at it with enthusiasm.