Bullying in school has shifted from physical attacks to psychological cruelty, say head teachers.
Head teachers say that phones are used in "psychological bullying"
The Secondary Heads Association has also strongly rejected the claim from the children's commissioner that schools are "in denial" over bullying.
Despite recent high-profile violent incidents in schools, the heads' union says schools are not ignoring bullying.
But the union's vice-president, Malcolm Trobe, says that "psychological bullying is more prevalent".
Mr Trobe, head teacher of Malmesbury School in Wiltshire, says that when he began his teaching career three decades ago, there was more physical bullying.
"Now there are more cases of verbal or psychological bullying. There are so many different avenues for this," he says.
Al Aynsley-Green is worried by cases involving extreme violence
Such psychological tactics have become common in the past five or six years, he says, driven by the near-universal ownership of mobile phones among youngsters.
"Mobile phones are used to send threatening messages or to ring people up and not saying anything. It all builds up pressure on youngsters."
As well as phone threats, he says children, particularly girls, have become more adept at ostracising each other and applying social pressure, by ignoring or excluding particular classmates.
But Mr Trobe says he would "strongly disagree" with the suggestion that schools were failing to take bullying sufficiently seriously.
Bullying exists in schools, he says, as it does elsewhere in society, including among adults in the workplace. But schools make determined efforts to identify and reduce the problem, he said.
The children's commissioner for England, Al Aynsley-Green had highlighted the scale of bullying in school. And he suggested that some schools were failing to pay sufficient attention to children's fears over bullying.
Professor Aynsley-Green told BBC News that children "put bullying top of the list of the things they want me to be aware of and they want bullying stopped now".
"It affects their lives in very many ways. It does seem to be a reality of their lives and they've obviously, in many cases, been badly affected by it."
And he warned that a series of violent attacks in schools, particularly involving girls, appearing to be a worrying pattern, in which pupils were ready to use extreme violence.
Last week, a 15-year-old girl in Surrey was stabbed in a school canteen. Last month, a 12-year-old girl needed 30 stitches in a face wound, after a classroom attack.
The president of SHA, Sue Kirkham, responding to the claim that bullying was endemic, said it was important to define what children meant when they used the term bullying.
"When a group of girls fall out, they might now call it bullying," said Ms Kirkham, head teacher of Walton High School, Stafford.
And she rejected the suggestion that schools were in a "state of denial" over bullying, when every school has a specific policy over tackling bullying.
"Far from being in denial, schools are very aware," she said. "Bullying has always existed, not just in schools, but elsewhere. But there is no magic answer."
Ms Kirkham also pointed to the problems caused by mobile phones, text messages and e-mails, saying that bullies used them without realising the seriousness of their impact on victims.