To introduce this lesson to second grade students, I first showed students two art works: Head of Dora Maar by Pablo Picasso and Senecio by Paul Klee. I wanted them to see these two very different treatments of the human face, and used them as references for contour drawing and use of shape and color. I then had them identify the qualities of portraits and self-portraits, then I modeled contour drawing using a black crayon on white paper, starting with an oval for the face shape. I pointed out to the students how hair grows down, not up, and emphasized that i was drawing the hair using only lines, and that nothing would be colored in with the crayons, since they would watercolor over the whole drawing.
Then I did something which really caught the students' attention: I drew the same exact face using a white crayon on white paper, pretending to ignore comments such as, "I can't see it!" and "Oh! I can see it just a little!"
I painted over the white face with watercolors using large blocks of color rather than following any of the contour lines. The students were surprised and excited about the way the white crayon resisted the watercolor paints, allowing the drawing of the face to show through. I explained to students that they would use only lines to draw their own face and then paint over their drawing with watercolor. I invited them to choose whether they would like to use black or white crayon, and talked about the use of the paints, explaining that they would need to use lots of water and avoid painting over painted areas. Since we were only using construction paper, rather than good watercolor paper, I knew it would be very easy for the paints to get muddy.
Most students chose to use black crayon, but a few brave souls opted for the white. The hardest part for many students was using large blocks of color rather than trying to "paint in" the face features or following the contour lines. I did encourage them to paint the background as well as the face itself, and in a few cases showed students how to paint across the lines rather than with the lines of their drawings.
Students enjoyed this activity very much, and they were very successful... and very, very quick! My classes are only an hour, but many students had time to do two self-portraits. I had those students try the second one using black if they had used white on the first, or vice-versa. I gave them time at the end of the hour to walk around to look at everyone else's self-portraits and to talk about other students' work... in positive ways, of course!