This paper analyzes the results of the study of prevalence of problem behaviour of students in primary and secondary schools. The starting point is that it is methodologically and logically justified to look for early forms of problem behaviour of students, because it is likely that adult convicted offenders at an early school age manifested forms of problem behaviours at school and in the society. Problem behaviours are classified into three categories: inappropriate behaviour at school; manifested anti-social behaviour and acts of violence. Results of the study showed that the most common forms were: (1) Antisocial behaviour: stealing, lying for personal gain, smoking, drinking and gambling; (2) Inappropriate behaviour in school: bored during classes; coming to school without adequate accessories and books for classes; not paying attention in classes and disturbing others in doing so; being late for school and coming to classes after the teacher; and (3) Acts of violence: conflicts with peers; insulting others; cursing and yelling in public areas; being involved in group fights; intentionally physically assaulted others. Comparison of these results with the results obtained by researchers at the sample of prisoners displays remarkable similarities, as prisoners at the elementary school level exhibiting the same characteristics: they lied to their advantage and to the detriment of someone else; consumed cigarettes; got drunk; gambling; involved in fights; socialized with aggressive people; were involved in group fights; inflict bodily harm to others, etc.