This study discusses the use of dynamic assessment for pedagogical purposes. Conducting dynamic assessment (DA), grounded in Vygotsky’s zone of proximal development (ZPD), we studied a group of Thai university students who had difficulties in speaking English. We adopted DA as an alternative assessment in the context of teaching English as a foreign language (EFL). This investigation is aimed at the students’ potential to improve their speaking skills in the test task called elicited imitation (EI). EI, which prompted the students to repeat sentences, was used to target specific features of the students’ English speaking in this study namely meaning, syntax, vocabulary, pronunciation, and fluency. Through the test-train-retest design, DA improved the students’ English speaking. The findings of both qualitative and quantitative data indicated positive impacts of DA on the students. Data from retrospective interviews and diaries showed that DA brought about meaningful learning experiences. The students also exhibited positive attitudes toward DA. The findings suggest that DA can be used in a classroom practice to promote development in the students’ English speaking ability.