My favorite art class to teach is drawing. I believe that drawing is the foundation of all other art forms. It's also one of the more difficult art skills to master. I tell students on the first day of art class that it's like magic. Drawing is creating an illusion of three-dimensional space on a two-dimensional surface.
To help students see and capture depth in their drawings, I like to do a lot of still life drawings in the classroom. Drawing a bone, in particular, is a great way to learn how to differentiate light and dark values. For this activity, I normally prefer using vine charcoal (which is really soft and brittle), but an all graphite pencil (shown below) is a lot cleaner and easier to handle.
I set up the lighting in the room so that there is only one light source shining on the bone. This creates lovely cast shadows, which are important to include in still life drawings. Since bones are relatively white, it's much easier to capture the variance of values on tinted drawing paper. For the lightest areas of the drawing, I instruct students to leave blank. Only at the last stage of the drawing will I pass out a white pencil or charcoal and have students highlight the brightest edges. A couple of other rules of thumb: try not to outline the bone when starting the drawing, and the darkest values should be on the subject itself, not the cast shadow.
Students are always surprised to find out how difficult it is to draw bones. I tell them that objects that look simple often times are the harder ones to draw. The lack of details in color and form push the artist to look for slight variances in other elements, like value.
If you're wondering where to find bones to draw, I actually found the one in the photos at an antique store! (It cost me $25, but I had to have it.) A natural place to find bones is the desert. Once I found an intact cow skull in Eastern Oregon that I hauled back to the classroom.
While we're on the topic of cow skulls, here's a beautiful painting of one by Georgia O'Keefe.
Cow's Skull with Calico Roses, 1931.