The present study investigates the relative contribution of the Nativeness vs. Intelligibility approach in prosody instruction for developing English speaking skills by Iranian interpreter trainees. Three groups of student interpreters were formed. Participants were assigned to groups at random. The speaking skill pretest scores revealed that the three groups were homogeneous before starting the training program. The Control group listened to authentic audio tracks in English, and discussed their contents, watched authentic English movies, and did exercises to improve speaking skills without receiving prosody training. The Nativeness approach group instead spent part of the time on the theoretical explanation of, and practical exercises in, English prosody with the overall aim to train students to acquire native-like speaking skills. The Intelligibility approach group spent part of the time on the theoretical explanation of, and practical exercises in, English prosody emphasizing the requirement that students produce intelligible speech. The total instruction time was the same for all three groups, i.e., 18 h. Students then took a posttest in speaking skills. The results show that both experimental groups performed better than the control group. Moreover, the Intelligibility approach group outperformed the Nativeness approach group in developing speaking skills.