Research has demonstrated that pronunciation teaching can be effective, but there have been very few classroom-based studies that have focused on the perception aspect of pronunciation. This article explains the theory and practical application of a conceptual approach and reports on its impact on perception of English word stress. The quasi-experimental study (N=18) involved four fifty-minute lessons on stress in two-syllable words in a high-intermediate ESL class. The experimental (n=10) group was tested pre, post (mid-semester) and delayed (end-semester) and the comparison (n=8) group was tested twice before receiving the instruction in the second half of the semester and being tested again. In line with a conceptual approach, the innovative testing method used moves beyond traditional identification tasks in an attempt to measure changes in participants' conceptual understandings. The tests showed large and significant gains in perception, which were retained eight weeks later. The comparison group made no gains, but after instruction improved on a par with the experimental group. This study presents an effective way of teaching pronunciation concepts, supported by theory, that also leads to improvements in perception. It informs and provides a template for both teachers and researchers who may want to replicate the study.