This study investigated whether task instructions affect sound-isolation performance. The effects of phoneme class and phoneme position were also assessed. Two hundred Dutch kindergartners were presented with a free-sound-isolation task and its constrained counterparts: an initial-, a middle-, and a final-sound-isolation task. All tasks contained 17 CVC words. Children's performance on the free-sound-isolation task was better than on the constrained tasks. On all four tasks, children made fewer errors in isolating the initial phoneme than the final phoneme. Isolating the middle phoneme proved to be the most demanding. The effect of phoneme class depended on the type of task and on phoneme position. Findings were placed against the background of sonority and word-final phoneme vocalization in Dutch. (Contains 1 table and 2 figures.)