SOOOO, thinking along the lines of empiricism, I looked up a few of Degas' works to help me understand the role of perspective in my own drawings. I love particularly his paintings of the dancer's in their practice studios because there are a variety of subjects and the fore/mid/background are very distinct.
In this particular piece, the foreground consists of two girls on the left hand side of the painting (one is sitting on a piano). They are large and prominent and don't block the mid and background, but rather frame the work and aid the eye's movement through the piece. The midgroundhas a few ballerinas walking along the edge of the room, but is mostly characterized by the male instructor who [I assume] is giving them instructions. In the background the girls are adjusting their skirts and getting ready to perform, but are much much smaller compared to the girls at the piano.
The perspective Degas presents is evident through various aspects in the painting. He uses linear perspective with the lines of the floor boards and the room itself to create a feeling of a receding space. He also uses empirical perspective by positioning himself in a [I think seated] position among the figures, and changing the size of the figures from the place where he is sitting in the foreground compared to the girls in the background. He places the teacher in the middle to establish a strong midground, and the teacher [as he should be] is smaller than the girls in the foreground.
I also like how he uses his impressionistic style to define perspective in the piece. Impressionism is characterized by "imperfect brushstrokes" and "unblended colors". In the foreground, Degas' subjects seem pretty clearly defined and have sharp edges about their clothing and bodies. However, as one's eye travels from the front of the classroom to the back, the brushstrokes become less defined, as if a near-sided person is looking at the scene. This difference in the quality of brushstroke adds another layer of depth to his painting, and maybe it would be useful or fun to try something similar in my drawing!!