This paper reports on a questionnaire survey of teachers' attitudes towards 16 selected undesirable behaviours carried out in all of the 79 state primary schools in Malta and Gozo. The responses of the 844 participants showed that stealing, cruelty/bullying and rudeness/impertinence are perceived as the three most serious behaviours in pupils. Significant boy/girl differences in the seriousness of behaviour were observed in 14 of the behaviours as rated by the total teacher sample, in 9 of the behaviours as rated by male teachers, and in 14 of the behaviours as rated by female teachers. The greatest boy/girl differences in the ratings of the behaviours was that for untidy in personal appearance as perceived by male teachers. Teacher-sex was also found to be a significant moderator of the teachers' attitude towards seven of the behaviours.