I love doing ZenDoodles with the kids. I show them YouTube clips of artist in superspeed creating these doodles. I explain to them that doodling uses the subconscious creativity. I compare it to "daydreaming with a pencil". I make them understand the they are not "drawing" anything intentionally. It is just using lines, shapes, patters, and designs. So, it is encouraging to tell them that they cannot mess up!
So, I make them use a pen to doodle. That way they cannot backtrack or try to "fix" anything.
After the doodle is completely filled up, I have them use a pencil and blendy stump to make some areas in the doodle appear 3D. I have them shade parts that would be considered underneath areas of the doodle.
They have fun and it is the most quiet class periods I have the entire year.
All of these are done by kids that range from 6-8th grade.
It does look nice on colored paper too, as long as it is lighter in color.
This bottom one is done by me as a teacher example of different ways of doing the doodle using colored construction paper with white and black colored pencil to shade.