I brought my class some Maple leaves, I found on a hike. I brought a variety of sizes and colors, greens to yellows to browns to show them how leaves are affected by season change and the position of the earth, relative to the sun.
We did a fun "Blind Contour" exercise with one leaf first, and it was amazing how well they did without being able to look at their paper, especially given all of the different directions and angles of the Maple leaf.
Then I held 4 different leaves up on a camera projector (awesome equipment wish every room had one of these!). They drew the leaf's outline shape, then the interior contours. Then...watercolor! I'm going to review basic watercolor techniques with some classes - as this turned out to be relatively messy, using too much water, or not enough. It WAS Halloween, though, when we did this lesson - maybe they were just super excited ! :)