This study addresses the diverse learning challenges in EFL speaking classes by implementing Differentiated Instruction (DI). Conducted over seven weeks, this classroom action research involved nine learners in a non-leveled EFL speaking class, each with varying initial English proficiency levels. Employing a participatory action research model, three cycles were used to develop, implement, and refine DI-based teaching strategies. These strategies were designed to address differences in content, process, and learning outcomes, utilizing tiered tasks, flexible grouping, and customized learning materials to meet the varied needs of the students. Data collection included pre-tests, progress tests, and post-tests, alongside student reflection journals and semi-structured interviews, to assess the effects of DI on learning processes and outcomes. The results indicated a significant improvement in speaking skills, with the Friedman test showing a significant effect (Chi-square = 25.93, p < .05, df=3, n=9). Additional insights were gleaned from students' reflections and interviews, providing further evidence of the positive impact of DI on student learning. These findings and their implications are discussed in detail in this paper.