Artificial intelligence is revolutionizing education, especially in language learning. This mixed method study examines how an AI-based application can improve the oral expression in English of 40 fifth-grade primary school students. Using the Design-Based Research (DBR) methodology, an AI-powered APP was developed and implemented over 16 weeks to support the development of oral English skills in the participating students. The results showed: a) a significant increase in student participation and motivation, b) notable improvements in pronunciation, fluency, and conversation skills, c) adaptability to the individual needs of students, and d) gradual progress in performance scores. The study highlights the transformative potential of AI in education, offering a personalized and effective learning experience. These findings are valuable for educators, educational technology developers, and policymakers interested in integrating AI into language teaching.