One of the first things I teach my Art 1 students is line. I start off with different line projects, showing them how a simple line can become sooo much more. I start off with line metamorphosis, this is the project where after repeating lines on a page they start taking on a life of their own, creating "waves" on the page. They do this assignment in their sketchbooks, along with several other line exercises.
Once we've completed these exercises we create several images using only lines. This is a slow going process at times but aside from the benefits the kids get from practicing line, it gives me the time to allow for schedule changes.
The kids are always amazed that they could create a recognizeable image using only lines.