Drawing is often used as a form of preparatory work to a painting, either in the form of sketches, finished drawings or initial drawings on canvas.
Drawing, however, also has great value in developing painting skills. It can build an awareness of structure, proportion and tone, all of which are essential to successful painting. In the past I have finished a life drawing session and then returned to a painting I was working on and suddenly noticed things that possibly needed improvement. Both pencil and charcoal drawing have great value, but charcoal is particularly suited to working with tone and can be moved and manipulated in a similar way to paint. It is, so to speak, a kind of 'dry paint'.
Drawing as an Art Form
Drawing is also a beautiful art form in itself, whether it be portraits, still life or the result of pure imagination. I would therefore recommend learning drawing, not only as a support to painting, but also as an art form in itself.
The lessons on drawing can be taken as part of the oil painting lessons or as a separate and expanded sequence of lessons so as to concentrate on drawing entirely. Both paths would include instruction on pencil and charcoal techniques.