Gryffindor: Changes background frequently, but they are usually cool-looking.

Hufflepuff: Turns the camera off but still listen to the lecture (camera-shy)

Ravenclaw: They are actually listening and taking notes down, and it looks like they're working when they are distracted. (They may be doing something else while looking serious)

Slytherin: Turns the camera off and does whatever they feel like doing. Don't tell them what to do.