In the last ten years the education system in Serbia has undergone a series of innovations which have encountered various obstacles. Teachers, as the key actors in the implementation of innovations, have implicit perceptions which may impact on the success of any school improvement. Therefore this study employed a mixed methods research strategy to investigate what teachers see as the obstacles to school improvement. A qualitative study implied four focus groups with teachers, while quantitative data was gathered through a questionnaire completed by 1,441 teachers from 40 primary schools from different regions around Serbia. Factor analysis confirmed that the potential obstacles could be grouped into six factors (Teachers’ incompetence, Material and organizational barriers, Lack of systemic support, Student related barriers, Lack of communication within the school, Lack of communication between schools and stakeholders). Teachers see the biggest obstacles to school improvement in student related and material and organizational barriers. Teachers do not see themselves as the most significant source of problems in improving the work of schools, but transfer responsibility onto more general issues and external agents. [Projekat Ministarstva nauke Republike Srbije, br. 179034: From encouraging initiative, cooperation and creativity in education to new roles and identities in society i br. 47008: Improving the quality and accessibility of education in modernization processes in Serbia]