To what extent do second language (L2) learners benefit from instruction that includes corrective feedback (CF) on L2 speech perception? This article addresses this question by reporting the results of a classroom-based experimental study conducted with 32 young adult Korean learners of English. An instruction-only group and an instruction + CF group were exposed to five 1-hr form-focused lessons that drew learners' attention to the nonnative phonemic contrast /i/-/?/, but only the instruction + CF group was given relevant feedback. Forced-choice identification tasks were completed by participants in a pretest, an immediate posttest, and a delayed posttest. The two groups showed similar accuracy on the pretest; however, the instruction + CF group outperformed the instruction-only group on the immediate and delayed posttests as well as on unfamiliar words. The significant predictors for these differences turned out to be perceptual accuracy vis-à-vis /?/-natural and /?/-synthesized sounds. These findings are discussed in terms of the pivotal role played by CF in developing accuracy in L2 speech perception.