Dynamic Assessment (DA) is proposed as a workable diagnostic tool in second or foreign language context. Compared to traditional non-dynamic testing, DA presents a more comprehensive account of human beings' abilities through addressing both the fully internalized abilities and the abilities that are in the process of being internalized. However, a major problem with the application of ordinary DA procedures is their limited capacity for addressing larger contexts in terms of learners and constructs. Computerized Dynamic Assessment (C-DA) is suggested as a solution for the practicality concerns associated with DA procedures. Considering lack of research in this regard, this study reports the results of designing and implementing an interventionist online computerized dynamic test of English listening skill for Iranian EFL university students. The online multiple-choice C-DA software has been designed following Poehner, M. E., & Lantolf, J. P. (2013). Bringing the zone of proximal development (ZPD) into the equation: Capturing L2 development during computerized dynamic assessment (C-DA). Language Teaching Research, 17(3), 323-342 and Poehner, M. E., Zhang, J., & Lu, X. (2015). Computerized dynamic assessment (C-DA): Diagnosing L2 development according to learner responsiveness to mediation. Language Testing, 32(3), 337-321. The software presents learners with ZPD-based mediation via hints and prompts and generates an actual score reporting their independent performance; a mediated score reporting their mediated performance; and a learning potential score (LPS) reporting the gain between the actual and mediated scores. The results revealed a significant difference between learners' actual and mediated scores indicating the inadequacy of non-dynamic testing in accounting for learners' responsiveness to mediation. Moreover, LPS could differentiate among learners classified into the same level by non-dynamic testing. The analysis of each learner's scoring profile plus their LPS proved conducive to diagnosing their strengths and weaknesses in different language constructs included in the test and could help teachers develop fine-tuned individualized learning plans and materials for future learning.