Purpose: Combining empirical insights from two lesson studies (LSs), this research aims to investigate EnEFL (English as a foreign language) teachers' development in understanding and practical skills regarding the recent national English curriculum reform in China. It also strives to incorporate students' performance and perceptions in the evaluation of the effectiveness of these LSs and teachers' development. Design/methodology/approach: Two LSs were conducted in the same school with 3 years in between. Standardized procedures were followed in the two LSs, including pre-LS interviews, talk-lesson session, rehearsal lessons, and one public lesson. Triangulated data were collected from lesson plans, reflective journals, discussion notes, and interviews to probe into teachers' learning and development. Students' task performance and perceptions were analyzed to help reexamine the influence of teachers' development on student learning. Findings: The teachers in the two LSs encountered similar problems in both understanding and implementing the curriculum reform. The LSs helped them reach a contextualized understanding of the key concepts. Besides, developments were also seen in their instructional skills to adopt innovative methods and activities. The students' task performance and perceptions endorsed the teachers' efforts. Originality/value: First, this research combines data from two standardized LSs at different periods of curriculum implementation in the Chinese EFL context, which provides insights into teachers' difficulties and development regarding curriculum reforms on a longer timeline. Second, students' performance and perceptions are included as important data sources to assess the effectiveness of the LSs and teachers' development.