EFL learners often have problems to speak properly in English. As the purpose of teaching speaking is to improve the learners' oral production, language teaching should maximize language use in the classrooms (Haozhang, 1997), which is achieved through implementing proper teaching techniques to require learners to learn and practice the language in EFL classes actively. Jeltova et al. (2007) know dynamic assessment (DA) as a process-oriented type of assessment which necessitates teachers and learners to interact while learners are provided with mediations based on their ZPDs. This makes DA potentially ideal for evaluating and scaffolding learners to expand their oral skills which are interactive (Son & Kim, 2017). The present study exploiting a quantitative approach, studied the effects of the Interactionist DA on developing learners' oral production while they interacted to perform language tasks. An experimental and a control group were selected, taught, and tape-recorded based on the techniques of the interactionist DA and the traditional methods, respectively. After transcribing and analyzing the data, the findings revealed significant development in the oral production and performance of the experimental group.