Young people are increasingly likely to carry knives to school and often believe it is acceptable to stab other teenagers - providing they avoid their hearts.
Reports from youth offending teams (YOTs) suggest that many young people who have been involved in knife fights do not understand that stabbings can be lethal.
Sir Charles Pollard, acting chairman of the Youth Justice Board, said "We have anecdotal evidence from Youth Offending Teams of young people attending offending behaviour reduction classes - sometimes specifically designed to tackle knife violence - apparently having no idea of the real impact of these weapons upon their victims.
"A YOT manager recently told me that most of the young people attending thought it was OK to stab someone in the buttocks, as this would not cause any significant injury.
"They believed that other than stabbing someone in the heart, a knife wound was not particularly serious."
Sir Charles added that YOT staff believed that cinema violence was partly responsible for the teenagers' blase attitudes. He quoted a team manager, who had said: "There is a complete area of unreality for these kids - they watch the films and do not realise the harm that can be caused. They really don't think that it's that serious."
The Youth Justice Board now plans to commission a study into whether there is any link between youth behaviour and violence in the media.
Sir Charles spoke of the concerns at a seminar on public policy at Queen Mary college, part of the University of London.
The former police chief said the young people's attitudes were particularly disturbing as they came in the wake of the murder of 10-year-old Damilola Taylor, who died in 2000 from a stab wound to the leg.
A recent study for the board by the criminologist Marion Fitzgerald, of the London School of Economics, found there are connections between youth crime and a perceived "need" among young people to possess the most prestigious model of mobile phone and other fashionable items such as trainers.
Dr Fitzgerald also discovered that young people who appeared to be unfashionable and weak were more likely to be picked on by their peers.