For decades, there has been a debate over the effectiveness of written corrective feedback in second language writing pedagogy. Recently, research on the issue has gradually turned from whether to give corrective feedback in L2 writing to how it can be effective; however, pursuit for effective pedagogical practices are still underway. To address this issue, the study reports on how contextualized feedback through teacher scaffolding can be effectively provided in L2 argumentative writing instruction and thus promote integrated development of language and cognition. Multiple data were collected to track students' learning processes, including classroom recordings, teacher feedback on students' writing samples, and teacher-student individual writing conferences. Results revealed a significant improvement in students' L2 written language accuracy and rhetorical genre skills and an evident progress in their language use appropriateness, though the rates of development can be subjected to individual language proficiencies. Results of the study can inform the development of an effective L2 writing pedagogy while shedding light on EFL learners' argumentative writing developmental trajectories.