The equivalent of one child in every classroom says they have been bullied face-to-face, or online, every day over the last six months, according to a survey.
A poll published by the Anti-Bullying Alliance (ABA) ahead of Anti-Bullying Week suggests 4 per cent of 11 to 16-year-olds are bullied on a daily basis.
Almost half (45 per cent) of the youngsters questioned said they had been bullied face-to-face, and 34 per cent online, at least once in the last six months.
More than four out of five of the children surveyed (87 per cent) reported seeing children bullying each other.
The majority (76 per cent) saw it at school, while one in three (34 per cent) witnessed it online, and more than a quarter (27 per cent) saw it in their communities.
As well as children bullying each other, the survey considered how many youngsters had seen adults engaged in the behaviour.
Forty-one per cent of the 1,000 children surveyed revealed that over the past six months they had seen adults bullying each other.
Almost all of them (97 per cent) said they would like adults to show more respect for each other, with 98 per cent saying showing respect is important and it is possible to be respectful even if you disagree with someone.
The children said they had seen the adult bullying take place face-to-face, online and in the media.
Martha Evans, director of the ABA, said: "Children who experience bullying are at higher risk of experiencing a range of mental health issues and leaving school with fewer qualifications.
"The impact of bullying can last well into adulthood.
"We need children to learn that we don't have to be best friends with each other or always agree with each other but this is never an excuse for bullying or hurtful behaviour.
"We are urging adults to role model the 'choose respect' message, and help us stop bullying in schools to prevent it from affecting so many children's lives."