The purpose of this study was to reveal the challenges and advantages of the implementation of the lesson studymodel in Turkish middle schools. This study was a case study and the participants of the study was 11 middle schoolmathematics teachers in three different school in a city at central Anatolia region of Turkey. Three lesson studycycles were carried out at one month. The data were collected with field notes, focus group interviews and anopen-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 wouldnot help their professional development. However, their prejudices were positively changed and they began to showinterest when they attended the implementations of lesson study. Implementation of the lesson study model enabledthe teachers to share experiences, to focus on students’ thinking / understanding, it also enabled teachers to be moreactive, 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 ofbeing observed, adaptation of students in research lessons, differences between researcher and teachers’ views aboutmathematics teaching, the intensity of the curriculum and the pressure of the central exam.