Dynamic assessment has been proven to effectively promote EFL learners' speaking proficiency, but its implementation in teaching speaking skills has been limited. One of the main reasons is that, thus far, very few studies have scrutinized the impacts of its two main models, interactionist and interventionist, on the speaking sub-skills of EFL learners. Instead of examining speaking as a general skill, this research focused on four speaking sub-skills, including grammatical range and accuracy, vocabulary, fluency, and pronunciation, with a concurrent experimental mixed-method design. To this aim, 30 undergraduate students from the Islamic Azad University, North Tehran Branch, were recruited through convenience sampling and participated in both phases. The quantitative data were collected from participants' pre-and post-test scores in the IELTS speaking module, and qualitative data consisted of the transcribed recordings of the intervention sessions. The integration of the quantitative and qualitative results revealed that while both models positively affected EFL learners' speaking proficiency, they differed in the extent and mechanisms of their impacts. The interactionist DA effectively improved grammatical range and accuracy, pronunciation, and vocabulary depth, and the interventionist DA enhanced fluency and vocabulary breadth more efficiently. The findings dissect the differential effects of DA models in one-to-one speaking lessons, offering practical insights for ELT practitioners and stakeholders.

动态评估已被证明可以有效提高英语学习者的口语水平，但其在口语教学中的实施效果有限。主要原因之一是，迄今为止，很少有研究审视其两种主要模型（互动主义和干预主义）对英语学习者口语子技能的影响。这项研究并没有将口语作为一项一般技能进行考察，而是侧重于四种口语子技能，包括语法范围和准确性、词汇、流利性和发音，并采用并行实验混合方法设计。为此，通过便利抽样招募了伊斯兰阿扎德大学北德黑兰分校的 30 名本科生，并参加了两个阶段。定量数据是从参与者雅思口语模块测试前和测试后的成绩中收集的，定性数据包括干预会话的转录录音。定量和定性结果的整合表明，虽然两种模型都对英语学习者的口语能力产生积极影响，但它们的影响程度和机制有所不同。互动主义DA有效地提高了语法范围和准确性、发音和词汇深度，而干预主义DA则更有效地提高了流利度和词汇广度。研究结果剖析了 DA 模型在一对一口语课程中的不同效果，为英语教学从业者和利益相关者提供了实用的见解。