He seems to focus on capturing a personal quality or an aspect of their personality. In conjunction with the environment or set where they are captured, which also plays part of their personalities. For example for this particular collection its about kids in the school most of the portraits are in a corner or against the wall. This could convey the message of feeling trapped on a social circle that is not of their nature or simply the feeling of self-consciousness.

Another aspect Bay uses to show their subjects personality  its posing. Arms crossed hi up showing a defensive side of their personality or leaning forward to show some attitude and self confidence.

The theme palette is colorful yet slightly muted.
Some portraits are warm while others are cold. He also uses color analogy for contrast. This helps drawing the eye to the subject’s character.

The rooms are well lid, the subject’s in this case teen students are mostly next to a window.
The lightning is soft and minimal almost as natural light from a window, which obviously seems to be Bay’s intention.