The present study tries to explore psycho-dynamics of Iranian EFL learners under the functions of dynamic assessment intervention modalities (i.e., facilitative vs. authoritative) modalities in developing their writing skills. To this end, this qualitative study ran on the basis of semi-structured interviews and written protocols data collected from 120 Iranian advanced EFL learners was designed to elicit an in-depth understanding of the participants’ thoughts during performing writing tasks. Thematic analysis of the qualitative data from both sources (i.e., interviews and written protocols) revealed that: 1) authoritative modality works more effectively in facilitating the processes of opinion expression and effective revision and correction, 2) facilitative modality contributes more to developing critical and reflective thinking processes while writing. In the light of the facilitative modality, the learners can easily switch from their individualistic focus to a collaborative culture among teachers and learners. So, the learners become more self-regulated and can move from object-regulation through other-regulation towards self-regulation. Then, EFL learners’ psycho-dynamic actions are a function of DA-modalities. The findings offer theoretical and pedagogical insights for both researchers and practitioners in addressing language learning and learners. تفاصيل المقالة