This paper aims to increase our understanding of the impact of Lesson Study (LS) on the quality of teacher learning. It draws on longitudinal and cross-sectional data from three waves of data collection from 214 teachers engaged in LS during one full school year. The findings showed positive effects of Lesson Study on meaning-oriented and application-oriented teacher learning and a negative effect on problematic learning. Less experienced teachers showed the highest gain in meaning-oriented learning. The paper contributes to advancement of our theoretical understanding of teacher learning as it provides evidence of mechanisms through which professional development impacts teacher learning.