I loved this exercise, even though it felt a bit daunting at first. Fitting all the students and teacher onto the paper I feel is the biggest challenge. I suggest grouping them as a whole to begin, sketching out one large shape and then going in and drawing in each figure as a shape. You won't need to get deep into detail on this exercise, it's more about focusing on the changes in value. Once you get it sketched out you can then begin to use light/dark values to fill the figures in. I worked on 11" x 14" and would love to do this exercise again but larger. I do feel the larger you work the easier it will be when it comes to adding the watercolor.
Check out this Flickr Pool for some great images to use for reference.
Supplies Used: Watercolor Paper. Pencil/eraser. Watercolor Paints