Behavioural difficulty is probably the least understood area of special education as it is very problematic to identify a specific cause. Behavioural difficulties are those behaviours that students sometimes exhibit that are inappropriate and unacceptable in the classrooms or schools, as they disrupt the smooth process of teaching and learning. This study investigated primary school teachers' perspectives of the causal factors of students' behavioural problems and what can be done to minimise this problem. The study was carried out in the Madang Province involving two primary schools. From the two schools, twelve teachers (six from each school) participated in the study. The same participants were involved in both the questionnaire and the semi structured interview. The data gathered for the questionnaire and interview were analysed and transcribed respectively. The findings discovered that the family and school factors contributed substantially towards students' inappropriate behaviours. Family factors include parental problems, abuse in the families, and the constant struggle to provide the basic necessities due to the high living cost. School factors, on the other hand, include negative teacher attitudes, teacher lack of knowledge and skills to adapt the curriculum to include social skills, lack of teacher support and encouragement, and peer influences. The findings also discovered that teachers were more bothered about externalising behaviours such as disruption and aggression than internalising behavioural problems like withdrawal and depression displayed by students. Further, teachers' limited pre-service and in-service training and lack of experience in teaching students with behavioural problems contributed significantly for teachers not attending to students who behave inappropriately. Based on the findings identified in the study, several recommendations were made on how to intervene to alleviate this problem. Of particular importance is teacher training at both the pre-service and in-service level. Also government support is needed in terms of funding for training, involving specialists and other resources to respond to student behavioural problems effectively and efficiently. The findings may have particular relevance to future studies in this area and provide teachers with effective and workable intervention strategies for students' behavioural problems in the classrooms.