This article was written concerning the problem of violent and aggressive behavior of students at the elementary school. The writing consists of three parts. The objective of the first part is to explain the meaning and definition of violence at the school. Here the author cited the definition found in literature. The second part describes the Prevention Program adopted by one of Warsaw's elemetary schools. Finally, the last part of the article contains the most important conclusion based on a conducted research. The main purpose of the research done in December of 2009 was to identify the reasons for violent and aggressive behavior of students at the school they were attending. A group of students from grades four through six were asked to fill out a questionnaire. The results were very interesting, as more than ninety percent of the polled students said they observed aggressive behavior towards other students at school. It turns out that verbal aggression is more common than physical one and that boys more often engage in the aggressive behavior than do girls. Also, it seems that aggression causes more aggression as a result. Almost 2/3 of the students that experienced violence were also aggressive to others.