There are three main reasons for this phenomenon in adolescents.
1. Partly it is the nature of the Age we live in, an Age of exceptional freedom and equality. Hence the old norms and patterns are gone and none of the old methods such as fear, punishment etc work.
2. There is lack of self discipline in the students as well as the teachers. The more a teacher exercises self-mastery the more he or she automatically exercises control over the students.
3. The subject itself may not be interesting or else presented in an interesting way that connects with the students. One should be creative and try to find better ways of engaging them with interesting examples.