I begin teaching the parts of composition in kindergarten. As the students get older, I reiterate these terms as much as possible. By third grade students start to put these parts into their artwork automatically without necessarily being directed to.
I created the Parts of Composition worksheet to reinforce the idea of foreground, middle ground, background and horizon line. I like to tell the students to imagine the painting as a window. If they crawled through the window, what would be the first thing they hit? Would it be large or small? Soon students are creating space and showing depth in all their drawings.