Almost one in three school students have suffered some form of bullying over the last month.
That's according to the United Nations, which is launching International Day Against Violence and Bullying in Schools today.
It says a person's physical appearance is the main reason for bullying, with people seen as different most often chosen to be a victim.
Additionally, there is "a strong connection and continuum between offline and online bullying".
The research also found that most students who are victims of cyber-bullying can report having been previously bullied in school, meaning many victims of bullying have suffered both online and offline abuse.
According to UNESCO, school violence and bullying is most likely to be carried out by students on other students but in some cases, it is perpetrated by teachers and other school staff.
The organisation says that corporal punishment is still allowed in schools in 67 countries.
Speaking today, President Michael D Higgins said it was "unacceptable that we would tolerate an atmosphere of anxiety, fear and insecurity" in schools.
He added that the UN's research shows "appalling findings of deep concern, demonstrating the need for heightened awareness of an issue that demands an appropriate set of policy responses to tackle its far-reaching consequences".
He said: "School-related violence, in all its forms, is a serious infringement, of course, of not only children and adolescents’ rights to education, but to their basic rights to health and well-being.
"The consequences of bullying include children and young people finding it difficult to concentrate in class, missing classes, avoiding school activities, playing truant, or dropping out of school altogether.
"The experience of being bullied has a demonstrable, adverse impact on academic achievement and intellectual and personal development, as well as future education and employment prospects.
He added: "Education at its best delivers security emancipation from sources of fear to children and young adults, such as will enable them to become free, responsible, engaged and participative citizens in an increasingly complex and interconnected world.
"Children are the future, they are agents of change within their own schools and communities, and they rightly continue to demand more urgent action on these important issues.
"We need strong leadership at every level, with public support, to tackle these issues which affect so many children and young people to the detriment of their education and quality of life, impacting on their future life circumstances and happiness.
"What is most important is acknowledging that we must address all the root causes of violence and promote a culture of respect for students’ rights and of zero tolerance to bullying and violence."