Shading
My advice is set up a still life. Use simple objects such as a white vase, white cup, or something similar that is well lit on one side. I know that is not the most interesting subject to draw, but the point is not to be thrilled by the subject, the point is for the shading beginner to have a simple object to study and draw with increasingly improved observation and accurate shading. A beginner can be anyone in any age group.
Evaluation
As the teacher it is your job to also observe the shading and reflected light of the still life. You will look at the student's finished work and offer constructive criticism.
Further Practice
Shading is a part of the entire drawing process and with that thought, when the student improves his observation and application of gradation and reflected light, then shading becomes included in assignments and in graded works that are planned. The student should draw from life as much as possible.
Ruskins Ultimate Assignment: Conquer the Stone
According to John Ruskin, if you can accurately represent an oval rock with ink or pencil, then you can draw anything because the world is as Ruskin says,
"For all drawing depends, primarily, on your power of representing Roundness. If you can once do that, all the rest is easy and straightforward; if you cannot do that, nothing else that you may be able to do will be of any use. For Nature is all made up of roundnesses; not the roundness of perfect globes, but of variously curved surfaces. Boughs are rounded, leaves are rounded, stones are rounded, clouds are rounded, cheeks are rounded, and curls are rounded: there is no more flatness in the natural world than there is vacancy. The world itself is round, and so is all that is in it, more or less, except human work, which is often very flat indeed."
Quoted from The Elements of Drawing, by John Ruskin
Instructions for Drawing the Stone
You may read this assignment in the words of John Ruskin at books.google starting on page 46 - a link: The Elements of Drawing, page 46. Please note that he writes about this exercise thoroughly, Read through pages 46 - 59 to understand the exercise in its entirety. It's not just shading or drawing A rock, you are drawing THE rock in front of you, the exercise implores the student to represent accurately the shape of the stone and the reflected light.
Related
John Ruskin's Book
The Elements of Drawing: in three letters to beginners.
Image of my copy of John Ruskin's Book (purchased from Amazon) If you decide to use it, you may download a pdf version from books.google or do as I did and purchase a hard copy.
There are two versions at amazon:
The one I have: digital images of the 1876 copy (is just like the google copy)
and
A facsimile reprint of the 1895 copy
I can't say what the difference is between the copies.
