This study used Latent Growth Curve Modeling (LGCM) to examine the overtime patterns of the score and test-taking strategy changes in an international high-stakes standardized proficiency test. To this end, the test records of 178 Iranian IELTS repeaters were analyzed, using close- and open-ended questionnaires to measure test scores as a function of construct-relevant and construct-irrelevant test-taking strategy changes. Additionally, this study explored the accountable factors for the changes in the repeaters' strategies. Results indicated a small and gradual increase in the test scores following an overall augmented use of test-management (TM) and a decreased employment of test-wiseness (TW) strategies. Along with contributing to IELTS validity evidence based on the repeaters' scores, this study found multiple sources to account for the changes in repeaters' test-taking strategies. Consideration of changes in repeaters' test-taking strategies by IELTS instructors and test users may add to the validity of interpretation of test scores to the intended purposes of the tests.