University entrance exams in Türkiye often generate significant test anxiety among high school students. This study investigates the effectiveness of a psychoeducational intervention based on Acceptance and Commitment Therapy (ACT) in reducing test anxiety among 10th-grade students. Employing a mixed-methods sequential explanatory design, the study included nine economically disadvantaged high school students (aged 15-17), two of whom were female and seven males, who participated in a six-session intervention. The quantitative phase utilized a quasi-experimental one-group pretest-posttest design, with measurements conducted using the Cognitive Test Anxiety Scale, the Mindful Attention Awareness Scale--Adolescent Form, and the Multidimensional Psychological Flexibility Inventory--Short Form. The qualitative phase comprised focus group interviews guided by semi-structured questions to explore participants' perspectives on the ACT-based psychoeducation program. The results demonstrated a statistically significant reduction in test anxiety and an increase in psychological flexibility, while no significant changes were observed in mindfulness levels. Qualitative analysis revealed three central themes: perceived benefits, most and least useful aspects, and suggestions for improvement. These findings suggest that ACT-based psychoeducation is an effective intervention for reducing test anxiety. Implications for future research and practical applications in educational and psychological contexts are discussed.