High school will always have the kids who prefer to be alone. They sit and read a book during lunch, do not always join in during a pep rally, and they appear to have very few friends. Yes, these behaviors could be a sign of shyness, but the person could also be an introvert. Introversion is not a negative trait, as many people are quick to assume. Some cultures and species value introversion above extroversion for a variety of reasons. Creativity is not always the best in groups; introverts may have the best ideas. A sense of calm is found in solitude and not the frenzy of a crowd. An introvert has just as many ideas about the world as an extrovert, and sometimes those ideas are more practical.
The majority of modern culture believes that two heads are better than none. However, creativity and sometimes productivity can actually decrease with additional heads. Group projects and decision-making can overwhelm introverts. As they pull away from the group, they are labeled as shy, which is a fear of social judgment. Introverts do not fear their peers. Instead, they have their own ideas and would rather quietly show than loudly tell.
The rush of a crowd and information overload can lead to a quickly overwhelmed person. Extroverts thrive in this situation, but they do not always work at peak performance. They may be spewing ideas and moving in a whirl, but their brain is running on overload and cannot function that way for long. An introvert will seek quietness in which to work. They do not need the constant re-affirmation of a crowd to know they are doing well. An introverted teenager will take less risks and present less promiscuity. Their actions are carefully thought out with very little room for failure.
The calm, in-charge introvert is valued in many cultures. Asian societies will actually reward introversion over extroversion, because they recognize the value there. Placing an introvert in a leadership role may not be as exciting as placing an extrovert. However, a record of achievement and fewer hiccups will appear. There are even valued introverts in nature. Some species value introverted individuals as a crucial part of survival.
So, before teasing the so-called shy teenager, ask their opinion on things and give them the time to respond. They will surprise you. The teenage years are full of strife and confusion. Calming down and focusing, like an introvert, could put things in perspective for a moment.