I agree with this.
I've been teaching art classes for a few years, and one of the main thing I always stress upon is the understanding of the basic shapes.
A lot of beginners don't know how to visualize in 3D.
Eg. A common beginner mistake is drawing a belt on a character straight across the belly instead of at a slightly curved angle because of the lack of understanding that the body is cylindrical.
Teach them how to differentiate between a circle and a sphere and other basic shapes is always immensely helpful.
Another way you can try is also to print a full body character at an interesting angle (but nothing too difficult) and get them to use a blue color pencil to draw the basic shapes, the center line etc, almost as if you're drawing the 3D topology of the picture.
Then get them to draw the same character in their own style by first drawing said guides.