The effective ways of error correction in teaching musical harmony have been neglected. Making students realize their mistakes and have them think over them are assumed to be helpful in harmony teaching. In this sense, correction code technique is thought to be beneficial for students to realize their mistakes and solve them on their own. Forty eight volunteer participants took a harmonization test and the experimental group received written corrective feedback via correction codes whereas the control group was corrected traditionally. This study was conducted to evaluate the efficacy of correction code technique on enhancing their understanding of 4-parts harmony. The results showed that experimental group improved more than control group between pre-test and post-test, F (1, 46) = 4.719, p < 0.035, ?2 = 0.051. Finally, students were asked open-ended questions allowing them express their feelings and reflect on the process. The data acquired from qualitative and quantitative parts of the study suggested that correction code technique was an effective way of error correction in 4-parts harmony.