We did this still twice -- although we were allowed to move around and find another view after the first one if we liked. The first one was a straight value drawing in charcoal. My first one went so badly that I never finished it. And no, I don't want to talk about it. On the second day, we started by covering our paper with a mid-tone gray and then "drew" in the highlights with a kneaded eraser. Only after all the highlights were lifted out did we go back in with charcoal and get the dark tones. I still have some work to do on the darkest shadows.
These things take so long! This was 2-1/2 hours.