EFL learners' oral proficiency plays an important role in the representation of their productive skills. Especially, English language learners' speaking skills are considered as main reflection of their proficiency in foreign languages. Speaking in L2 is accepted as a vital competence for language teachers as well, who are going to teach the target language in the future. The related literature puts an emphasis on the assessment of speaking skills utilizing various techniques. However, the number of research studies, examining how dynamic assessment (DA), especially the interventionist model of dynamic assessment, can be utilized as a technique in the assessment of L2 speaking performance, is relatively limited. Thus, the main aims of the current research study are both to investigate the efficacy of the interventionist model of DA in the assessment of student teachers' speaking skills performance and to figure out their attitudes towards dynamic assessment. The participants of the current research were 29 student teachers, enrolled in the English Language Teaching Department of a state university in Turkey. To collect the quantitative data questionnaire survey was adopted and utilized as a checklist due to the number of the participants. On the other hand, to collect the qualitative data, a written structured interview was administered to the participants. The data were analyzed with the SPSS package and through the content analysis method. The findings of the current research revealed that participants were satisfied with the interventionist model and developed positive attitudes towards this assessment type. The participants stated that the interventionist dynamic assessment provided an authentic, creative and relaxing atmosphere, which decreased the level of their speaking anxiety. It can be asserted that DA can be administered to test foreign language speaking performance in language classrooms. Additionally, it was concluded that the interventionist model sustained and boosted the student teachers' oral skills achievement.