The study aims to develop students' higher cognitive skills e.g. analysis, synthesis and assessment and to increase their academic successes by reflecting their cognitive skills in psychomotor skills in practice with the help of lesson study. Therefore, the aim of the study is to increase students' English as a foreign language learning level. Action research was used in the study. "English Achievement Test" and "Semi-Structured Interview Form" developed by the researchers were used as data collection instruments. English achievement test was used as pre-test and post-test to define students' English language levels, and semi-structured interview form was used to determine teachers' views about lesson study practice. According to research result, lesson study has increased students' learning levels significantly. Moreover, teachers stated that lesson study was highly beneficial and affected their professional development in a positive way. It was stated by teachers in the study that lesson study had the teachers a chance to observe and assess their teaching qualities and so, it made the students' learning levels increase significantly. Furthermore, all of the teachers agreed that lesson study as an in-service training model could be an approach used for both other lessons and nationally.