Dynamic Assessment (DA) has lately taken the floor as an alternative by embedding instruction into assessment. Grounded in the dialogic teacher-learner interaction during an in tandem work, DA asserts that diagnosing the learners' matured abilities and needs, mediating them accordingly, and then observing their maturing abilities and microgenesis are crucial. This assertion paves the way to reveal each learner's Zone of Proximal Development (ZPD). Despite some influential studies on the use of DA in language education, more studies are warranted to explore the use of DA in different contexts and with different participants. Therefore, this case study recruited two multilingual immigrants/refugees who were underachievers in L2 writing classes. They were provided individual interactive DA for ten weeks, and the dialogic interactions between the teacher and the students were analyzed. Initial results revealed that the mediational moves mainly rested on teacher-agency, but over time more learner-agency-oriented mediational moves were also adopted. Furthermore, these students started to narrow the gap between themselves and their classmates. Lastly, a semi-structured interview was conducted to illustrate the participants' perspectives towards DA in the L2 writing context, and the related data revealed recurrent themes that had bidirectional relation with DA's theoretical premises.