The study aimed at analyzing the influence of Differentiated Instruction (DI) on learners' autonomy levels in English writing at the secondary school level. Employing a true experimental design, the research examines the causal association between the independent variable (DI intervention) and dependent variable (students' autonomy level). Random assignment of eighty students from grade-9 to experimental group (n-40) and control group (n=40) ensures equitable distribution and minimizes bias. The DI intervention, implemented over 12 weeks, includes various strategies such as designed lesson plans, flexible grouping, and personalized feedback. Pre- and post-tests, utilizing a standardized autonomy questionnaire, assess students' autonomy levels. Statistical analysis, including individual sample t-tests and paired sample t-tests, evaluates the effectiveness of the intervention. Findings indicate a significant positive impact of DI on student autonomy, suggesting its importance in promoting student engagement, motivation, and proficiency in English writing. Conclusions emphasize the integration of DI practices, collaborative lesson planning, continuous assessment, and technology integration to foster an inclusive and supportive learning environment conducive to student autonomy and academic success.