In clas, American teachers also want their students 100% concentration, and by this they mean to look at them, or have eye contact. It's so important of the eye communication in American classroom that they believe this is the way of respect and concentration. In many literary works, eyes have been a very fascinating topic. Shakespeare had these words: "Thou tell'st me there is murder in mine eye." Bob Dylan also had "Your eyes said more to me that night than your lips would ever say." Therefore, in western cultures, eye contact is highly valued. If you don't have eye contact with an American, it's very likely that they interpret this as a sign of disrespect, lacking self-confidence, or even lying.