This diploma thesis deals with behavioural problems of pupils in a school setting, particularly with aggression and bullying, as well as the possibility of their prevention. It consists of a theoretical part, a practical part, and appendices. The theoretical part treats behavioural problems in pupils, presenting the separate disorders in all their possible forms, accounting for both internal and external factors triggering them, explaining their causes and the conditions under which they occur, and, finally, surveys the possibility of their prevention and treatment. The practical part uses a questionnaire designed by the author of the thesis and discussions conducted in schools to identify the most common types of behavioural disorders. The results of the research are presented in charts and graphs and are complemented by data obtained in the discussions. This part is concluded with a thorough analysis of the data. The appendices contain real-life examples of behavioural problems encountered by teachers, the minimum prevention programme implemented by the basic school in Jistebnice and its evaluation for the school year of 2008/2009, the crisis management scheme of the same school, and additional materials relating to the topic.