This study focuses on the application of dynamic assessment (DA) for pedagogical purposes. It is aimed at investigating how the students' English speaking skill could be improved through DA, which is grounded in Vygotsky's zone of proximal development (ZPD). The objectives of this study were (1) to investigate to what extent DA assists EFL undergraduate students to improve their English speaking skill, (2) to explore the students' perceived self-efficacy in their English speaking skill through DA, and (3) to examine the students' attitudes toward DA. The participants of the study were 10 university students who studied in an EFL classroom of Foundation English I (ENG 101). Both qualitative and quantitative research instruments were employed in this study. As for the qualitative instruments, the participants' verbal report, semi-structured interviews, and diaries were adopted. The quantitative instruments employed in this study were the three tests (pretest, posttest, and delayed posttest), a self-efficacy questionnaire, and an attitude questionnaire. The results of the study revealed that through the test-train-retest design, DA improved the students' English speaking skills and their perceived self-efficacy toward English speaking skills. The data from qualitative instruments showed that the participants gained meaningful learning experiences through DA procedures. All participants expressed positive attitudes toward DA. The results of this study indicated that DA encouraged the students to construct a sense of ownership in their own learning and to become actively engaged in the test tasks. Thus, this study has shed light on the possible application of DA for a remedial classroom in an EFL context.