Present study focuses on revealing and developing personal constructs regarding problem behaviour in classrooms. The main idea is that teachers opinions about their students and themselves influence the way they interact with them. Their thoughts and ideas about students - their personal constructs - are generally unconscious. We used the Personal Construct Theory from Kelly (1955) and his Repertory Grid Technique for exploration mental constructs. They can give an impulse to the development of thinking and acting of teachers. We think it can help them to build up their professional identity towards problem children. Twenty-nine teachers formed the sample that worked with this method. We investigated the number of unique construct pairs mentioned by the teachers. This number happened to be remarkably high. While assessing pupils, the teachers use primarily personality characteristics. There is hardly any agreement between the teachers constructs, which complicates their communication about their pupils. We considered the number of construct pairs named by one participant. This number seems to depend on the type of education the teacher is involved in. The type of the school the teacher is working at also influences the average scores on the constructs. We shall also turn to the issue of pupils sex and its role if any in the teachers scores. No significant differences have been found.