The purpose of this study was to investigate the primary and middle school English language teachers perception and practices of lesson study (LS) in improving their professional development and classroom practices in Bahir Dar City Administration. The study also investigated the impact of LS on teachers’ professional development and their classroom practices and challenges affecting the implementation of LS. For this purpose, a mixed methods research approach and quasi-experimental design was used. The major data sources were primary and middle school English language teachers of Bahir Dar City Administration. Questionnaires, interviews, and observations were used to collect data pertinent to the study. The quantitative data were analyzed using percentage, mean, standard deviation, paired sample t-test and independent samples t-test. On the other hand, the qualitative data were analyzed through descriptions and narrations. The findings of the study revealed that the experimental group teachers, who took part a six weeks of intervention, in the LS sessions, had shown better perceptions on LS compared to those teachers placed in the control group. The findings also disclosed that those teachers who participated in the LS intervention have a positive impact on teachers’ professional development and classroom practices. The results obtained both from the quantitative and qualitative data revealed that those teachers who took part in LS performed better practices in preparing, enacting, and reflecting on their contents and subject plans. Moreover, the paired sample t-test result indicated that there is a statistical significant difference in the mean score values of the post-test and the pre-test revealing a better post-test results. The independent sample t-test result also revealed that there was a significant difference in the post-test results between the control and experimental groups. viii The results of this study implied that collaborative work among teachers through LS is an appropriate strategy to improve teachers’ perceptions, classroom practices, and professional development. Hence, it is reliant suggest LS as a useful capacity building strategy for the professional development of primary and middle school teachers of Bahir Dar City Administration.