Classroom management is considered as one of the most important factors in facilitating successful teaching and learning. Many studies suggest the in-service training of teachers as a solution to improve teacher performance in this area. In developing countries, researchers and educators often suggest the importation of ideas and programmes from developed countries which have a high quality of education. However, in order to gain the desired results of any programme, the factors affecting implementation should be considered. This study examines these factors by looking at the implementation of an international and highly effective intervention programme, âThe Incredible Years Teachers Classroom Management Programmeâ (TCM) which was developed in the context of the US and implemented in primary schools in Saudi Arabia. Three case study teachers from different schools participated in this qualitative study. They were teaching in schools that were located in three different zones; the city, the village and the desert. The teachers attended a full six days training programme about the TCM facilitated by the researcher over three months. Data was collected to investigate its implementation. Each training day was followed by an observation and feedback interview. Further teacher and expert focus groups were conducted to enrich the data. The expert focus group included headteachers, educational supervisors and studentâ consultants. The findings show that at all levels there are many factors which affect TCMâs successful implementation. These factors interact together, affect each other and impact on the teachers' implementation in their classes. Individual level factors include a lack of teacher willingness to implement the programme, a lack of teaching skills and efficacy, and negative teacher attitudes towards students, schools and teaching. At the school level, a demotivated school climate, passive headteachers and large numbers of students in the classrooms were included. While the education policy, motivation system, curriculums, community and culture were the main factors at macro level. The study concluded that unsatisfactory implementation will be expected whether for TCM or any other programme unless contextual factors that demotivate teachers are addressed.