The role of corrective feedback in general and focused feedback in particular has been investigated widely in second language (L2) writing over the past several decades. Moreover, Dynamic Assessment (DA) with its roots in socio-cultural theory has been noticed to play a role in fostering language learner development and assessment. However, their differential effects have rarely been investigated. Thus, the present study was an attempt to explore the impact of dynamic assessment (DA) and Coded Focused Feedback (CFF) on the Iranian EFL students' writing performance. To this end, two experimental groups of high intermediate learners were selected to compare the effects of assisted writing instruction through Dynamic Assessment (DA) versus unassisted feedback (CFF) on their process writing. A mixed method analysis was used to answer the research questions. Students' performance on pre-test and post-test were analyzed via paired sample t-test and independent t-test. Transcripts of the teacher-student interactions in the DA group were also used to analyze the data further qualitatively. Results of the t-tests (p= 0.00aZ5 T=-7.415 and p= 0.5 T=-1.0) and the descriptive study of the transcripts indicated that the DA group outperformed the CFF group both in the process writing and the revisions of the assigned topics implying that assisted writing instruction through DA helped learners to improve their writing ability. A careful design of the study via the sequential mixed-methods approach enhanced the originality and strength of the present study. It concluded that scaffolded assessment through dialogue would result in improvement in students' process writing performance.