It is scientifically proven that stress causes you to break out in pimples. In other words the more homework and tests you have (and other things that may stress you out), then the more pimples you will get. Completing homework early on and not leaving things to the last minute (very stressful) will ultimately lead to a less stressed lifestyle, and thus a less pimply face.
That is just one affect of stress for teens, but it is highly obvious physically.
Not really psychologically, however pimples aren't good for anyone's self-esteem.
Good Luck!
- TrustworthyOnes