Do young people model their behaviour on adult delinquents?
Parents and adults too often set a bad example for young people, says a head teacher who is to publish a report on tackling bad behaviour.
Sir Alan Steer suggests that adults need to take responsibility and not provide bad role models with behaviour that is greedy and aggressive.
Sir Alan has been carrying out a review of behaviour in school since 2005.
A survey from the General Teaching Council shows that bad behaviour is the biggest reason for teachers quitting.
Sir Alan, head teacher of Seven Kings High School, Ilford, is due to publish further findings from his government-commissioned report on behaviour.
It comes against a background of growing concern over teenage knife crime - and Sir Alan highlights the responsibility of adults in creating the cultures of good and bad behaviour.
Sir Alan told the Guardian: "It's connected to a violent sub-culture. But we bear some responsibility. Sometimes as adults we don't model the behaviour we would want youngsters to follow. We live in a greedy culture, we are rude to each other in the street. Children follow that."
Last month, Schools Secretary Ed Balls warned that parents had to "play their part" in promoting better behaviour.
"When I talk to heads they say behaviour is one of their main concerns. Some talk of giving detentions to pupils only for the parent to come in and demand their child is let off," Mr Balls told a meeting of school leaders.
"So whilst the vast majority of parents work really well with schools, a small minority are not supporting heads to maintain discipline."
The interim report from Sir Alan, due to be published on Monday, is the latest instalment of his work on improving behaviour.
Sir Alan reported in March that good progress was being made in tackling bad behaviour - and he highlighted a range of important influences on behaviour.
These included the quality of teaching, clear and consistent rules, mutual respect and the support of parents. But he cautioned against assuming there were "simple solutions".
Concern about poor behaviour by pupils has been identified by the General Teaching Council as the reason that teachers are most likely to leave the profession.
The survey found that about four in 10 teachers leave the profession after two years.