The purpose of this study was to reveal the challenges and advantages of the implementation of the lesson study model in Turkish middle schools. This study was a case study and the participants of the study was 11 middle school mathematics teachers in three different school in a city at central Anatolia region of Turkey. Three lesson study cycles were carried out at one month. The data were collected with field notes, focus group interviews and an open-ended questionnaire. Data were analysed by using content analysis. Moreover, direct quotations from teachers' views were also included. Findings indicated that teachers had prejudice that the lesson study implementations would not help their professional development. However, their prejudices were positively changed and they began to show interest when they attended the implementations of lesson study. Implementation of the lesson study model enabled the teachers to share experiences, to focus on students' thinking / understanding, it also enabled teachers to be more active, to examine the curriculum and resources related to instructional materials in depth. On the other hand, challenges in the process of lesson study implementation were as follows: time problem, teachers' ego and fear of being observed, adaptation of students in research lessons, differences between researcher and teachers' views about mathematics teaching, the intensity of the curriculum and the pressure of the central exam.