International research investigated fourth class students' behaviour and how bullying impacted on their schoolwork.
An average of three students for every class of 24 said that they have experienced three types of bullying behaviour once or twice a month.
This includes being hit or hurt by other students, being made fun of or being called names, having lies spread about them, having something stolen or being left out of games.
The results were published this month as part of the International Association for Evaluation of Educational Achievement tests in reading, maths and science.
Researchers said that there were serious problems with the emerging form of online and mobile phone bullying.
"There is growing evidence that bullying in schools is on the rise, especially with the emergence of cyberbullying, and that bullying does have a negative impact on students' educational achievement," the group said.
In a survey of 4,500 Irish 10-year-olds, 12pc said they were bullied at school 'about weekly'.
This means that at least three children in every primary school fourth class are being bullied every week.
Ultimately this has a negative impact on schoolwork, the research has discovered.
On average, an Irish 10-year-old scored 552 points in reading, and for children who are almost never bullied this jumped to 563. However, for those bullied monthly the average score dropped to 545.
And any child who reported being bullied on a weekly basis saw their score plummet to 510.
Differences in maths and science scores are almost identical, falling by more than 50 points when comparing pupils who are bullied weekly to pupils who are almost never bullied.
Although one eighth of every class said that they are victims of bullying, the investigation uncovered that regular bullying in school is less common in Ireland than in most other countries.
And about two-thirds of students say that they are hardly ever bullied.