Here is a drawing from another one of my "homework" classes at the Watts Atelier. The class, focusing on drawing portraits from photos using charcoal and graphite, was taught by Stan Prokopenko.
In the basic method the general contour lines of the portrait are roughed in with a fairly dark lead, like a 2B. Next the areas of darker value, including the background, are filled in with powdered charcoal using a large paintbrush. The image is then worked up using graphite pencils and picked out with a kneaded eraser. The nice thing about this method, for anyone whose done large-scale graphite drawings, is that the fill-in of darker areas and backgrounds goes much faster without loss of detail or quality, so you can focus on the fun stuff. This portrait took about 8 hours to complete.
My source photo for this drawing was from the Phaidon Press book "Portraits" by Steve McCurry. A nice book to add to your art library as it's loaded with great images suitable for drawing and painting.
African Boy 2008, graphite and charcoal on bristol board, 10 x 6