Start with an exercise in pattern to prepare the students for the tedious task of scale-making. You're gonna need a good "flow" to keep them on it. Follow up with a geometric-shape constructed drawing with a light pencil on dark paper (black with white pencil in this case). Begin drawing details. Start with highlights, go backward with colored mid-tones. Complete a value scale with six shades if necessary, and it probably will be even if just for reminding. Aim for smooth gradation!