Continuous professional development is a process that requires constant and active learning for a teacher throughout his/her professional life. In this process, teachers are expected to perform activities aiming at increasing both their professional development and the quality of teaching within the classroom. One of these is lesson study. This study examined the effect of the lesson study as a tool to improve professional development of teachers, as well as student learning. Case study, one of the qualitative research methods, was used. Participants were two primary school teachers. Data were obtained from observations and field notes taken during the teaching of the course alongside data coming from teachers' reflective diaries and interviews held with the teachers. The findings of the study showed that the lesson study activity contributed considerably both to the professional development of the teachers and the students' learning. Thanks to the student-centered activities (narration, picturizing and drama) which were carried out within the scope of the applied research lesson, almost all students in the class were actively involved in the lesson, especially those who had relatively worse reading comprehension skills and who had difficulty in self-expression started to give better answers and also expressed what they read in a better manner. In addition, teachers stated that lesson study contributed to their professional development by helping them solve the problem they faced paving the way for the application of different teaching methods and activities, collaboration with each other, exchanging of opinions about the problem, and recognizing different methods, techniques and practices pertaining to the profession.