Conventional ASSESSMENT methods have faced widespread criticism, highlighting the need for alternatives like DYNAMIC ASSESSMENT (DA). This study examines the efficacy of two types of DA, interventionist and interactionist, on grammatical accuracy in writing. A total of thirty-eight Iranian EFL (English as a foreign language) learners whose ages range from 18 to 30 and include both males and females participated in this study at Paymeh-Noor University in Tabriz, Iran. Convenience sampling technique was used, selecting two existing intact classes to preserve a natural classroom environment. Their initial homogeneity was established based on scores obtained from the Preliminary English Test (PET). The participants were randomly assigned to two experimental groups: one receiving an interactionist ASSESSMENT and the other receiving an interventionist one. The intervention spanned ten sessions of ninety minutes each, during which all groups experienced identical instructional procedures and received the same instructional materials. Upon completion of the course, all the participants completed a parallel form of the PET as the post-test to assess their progress. The analysis of the scores obtained from the pretest and post-test revealed that learners who participated in interactionist DA showed significantly greater improvements in grammatical accuracy in writing compared to their interventionist counterparts. This study highlights the value of interactionist DA in language education, highlighting its capability to deliver personalized, real-time mediation aligned with learners' needs. By promoting active participation and ongoing formative feedback, interactionist DA enhances language development more effectively than interventionist approaches. Educators should adopt this learner-centered framework to boost responsiveness and outcomes.