Research on second language (L2) writing tends to focus much more on student learning of writing than teachers’ teaching and learning of the teaching of writing. While a few studies have considered the influence of formal education on teachers’ L2 writing instruction, such as by examining the changes in teacher beliefs and practices across one semester (Lee, 2010), little is known about the long-term impact (e.g., 2 or 3 years) of such training on the professional development of L2 writing teachers. The present study adopted a multiple-case study approach to examine the long-term effects of a course on teaching L2 writing on five teachers of writing who taught writing in different contexts (primary school, secondary school, private language training center, and university) in the Chinese EFL context and how the teachers may apply the theoretical knowledge and recommended pedagogies presented in such a course. Drawing upon multiple sources of data, including interviews, stimulated recalls, and teaching materials, this study revealed that despite the peripheral position of writing in current L2 literacy education, training teachers to teach L2 writing can have both immediate and lasting effects on their thinking, practices, and learning as L2 writing teachers. The course enhanced the teachers’ understanding of L2 writing and writing instruction and enabled them to adopt new pedagogies and feedback practices, whereas previously they had neglected writing instruction and taught writing based on their prior learning experiences. However, the teachers’ teaching experience determined their appropriation of the new pedagogies when contextual constraints such as students’ language proficiency, limited class hours, and exam pressure hindered their adoption of the changes. The study draws attention to L2 teachers’ knowledge gaps (thinking), their teaching practices, and their learning to teach writing (learning) and elucidates the impact of educating language teachers to teach writing across various educational settings.