The effective management of pupils' undesirable behaviours in the classroom represents a major challenge for teachers. In order to better comprehend the difficulties facing them it is important to examine how they perceive pupil behaviours at different stages of their professional development. The present study examined the effects of teaching experience and pupil and teacher gender on student teachers' perceptions of the seriousness of various forms of undesirable behaviours. A structured questionnaire was completed by 243 student teachers, regarding the perceived seriousness of 25 behaviours in boys and girls. Results indicated that both teaching experience and pupil gender were important moderators of their perceptions. For instance, novice student teachers rated overtly antisocial behaviours as serious, whereas their experienced counterparts gave higher ratings of seriousness to internalising forms of behaviour. A degree of gender stereotyping was also apparent in the perceptions of mainly novice teachers. The accumulation of teaching experience may help direct teacher attention to more subtle aspects of pupil behaviour difficulties and may reduce gender stereotyping.