Fare dodging and shoplifting were among the most common offences
One in six young people has been involved in a "happy slapping" attack, a survey has suggested.
The 11- to 16-year-olds said they had either recorded or photographed an assault, the Mori poll for the Youth Justice Board (YJB) revealed.
A total of 4,750 pupils from 194 English and Welsh schools took part.
Crime involving girls had risen 10% during the past three years, while the number of boys committing offences dropped 6%, the figures indicated.
Among pupils questioned, 22% said they had used their mobile phone to send a voicemail or text designed to scare, harass or threaten someone. The percentage among girls was 26%.
It was the first time youngsters had been asked about mobile phone-related crimes.
Almost a third of those questioned - 45% of boys and 16% of girls - admitted carrying a knife or gun, usually penknives and ball-bearing guns, in the past year.
Sports, hobbies and "protection" were the reasons most commonly given for carrying a knife, though few said they intended to use it.
But the frequency with which pupils admitted offending had fallen from 27% in 2005 to 23% over the past year, amounting to 17,143 fewer crimes, the poll said.
YJB chairman Frances Done said: "This survey shows the majority of children are law abiding and know right from wrong.
"Unfortunately there is still a minority that can blight the lives of their community with their offending."
In relation to the proportion of girls getting involved in crime, she said: "Many of these young women have had difficult childhoods... been abused or seen violence in the home."
The three most common admitted offences were fare dodging (53%), shoplifting (45%) and hurting someone who did not need medical treatment (42%).
Boredom was again the most common reason given for offending (25%) but more youngsters mentioned alcohol or peer pressure as related causes.
A total of 59% said they had tried alcohol at least once in their lives, but fewer (37%) said they had used it in the past month.
Ms Done added: "We aim to provide better and earlier prevention which challenges boredom, improves pupil confidence at school and helps resolve conflict that could escalate outside the school gates."
The research was carried out between 21 January and 11 April 2008.