In addition to learning drawing from observation, I have students learn grid drawing. It works in a similar way, but may be easier since it breaks down an image into smaller, possibly more abstracted tasks.
For ours, I pre-selected some images, and used http://www.griddrawingtool.com/ to automatically apply a 4x6 grid of squares. If students wanted a different image, it was easy enough to pump it into the online program and print out in a minute or so.
our drawing paper is 12- 18 inches, so a 3 inch grid works with a 4x6 matrix.
In fact, I made a classroom set of grids that students could place under their drawing so they did not even have to draw the grid! They could see the grid lightly through the drawing paper.
We had not talked about color yet, so these were finished with pencil and we focused on value.
Grid Drawing Rubric:
Accurate drawing 40 points
Full range of Value 30
total 100 points
Here are some of our results.