Background: Teachers' writing proficiency and writing assessment ability and their role in improving writing instruction in second language learning classrooms are issues that have not been investigated empirically and rigorously. To bridge the gap, we investigated the writing proficiency, writing assessment ability, and written corrective feedback beliefs and practices of Iranian English teachers who gave feedback on learners' writings. Methods: To this end, 103 Iranian teachers who had the experience of writing instruction and assessment in their classrooms completed two writing tasks, assessed and gave feedback on two writing tasks, and responded to a researcher-made questionnaire inspecting their feedback beliefs and practices and research interest. Results: The data analysis showed that the teachers' writing proficiency did not satisfy the expectations and standards. Their writing assessment ability was also not accurate. Moreover, the data obtained from the questionnaire indicated that the teachers mostly gave unfocused direct written corrective feedback; they did not use technology in writing instruction; and most of them did not ask the learners to revise the texts which received feedback. Furthermore, the results showed that a majority of the teachers did not study the research papers because they did not have time and lacked access to the journals. Conclusions: As the findings of this study showed, more research is needed to improve the quality of writing instruction in Iranian classroom context. More research seems necessary especially in different contexts to come up with practical suggestions for teachers who give WCF on their students' writing and assess and grade writing. These are critical issues that merit investigation in future research.