One of my goals this year was to help students understand simple ways to show space in their artwork. I had some students put their hands together and say "space" as they moved their hands apart to remind them that in art, space means distance.
With 1st-3rd grade, we talked about layers and overlapping being simple tools for developing space, as well as making objects in the distance smaller and higher on the paper. Even just raising the horizon line a little bit above the focal point instead of having that focal point (a house, a person, etc.) on top of the line creates a bit of distance. Lots and lots of students have all of a sudden become interested in landscapes.
There have been a lot of drawings as well as some wax-resist and mixed media paintings.
It has really made a big difference in improving their compositions!