My 3rd grade students learned to show different values with watercolors, by varying the amount of water with their paint. The lesson went extremely well!
The first day, the students traced yogurt cups to make several circles on their paper. I told them to make at least four, in case they messed up on one.
Then, the students painted a pale oval on one edge of a circle, without filling it in. A medium hue was used in the middle of the ornaments, and a dark value was used in a crescent-moon shape on the other end. The students tested their values out on the edge of the paper; it takes practice to get just the right shade!
The second day, the students cut out their three best ornaments, and glued them on a black paper. They used construction paper crayons for the evergreen branches, and metallic crayons for the ornaments' hanging mechanism.
It was a very successful lesson; I think all of them turned out beautifully! The photos are a bit washed out, though, and don't show the vivid colors very well.