Hoonmil Kim (2025). A longitudinal study on quantitative changes in students’ fidelity and fluency observed in English-Korean simultaneous classroom. This study examines changes in fidelity and fluency in English-Korean simultaneous interpreting among graduate students over two semesters. While average fidelity scores remained stable (61.7% to 62.8%), modest improvement was observed when adjusting for outlier performance (61.7% to 66.0%). Notably, lower-performing students showed significant gains, while higher performers plateaued, suggesting they had reached their performance ceiling by the end of the first semester. Fluency, measured by speech rate, improved by over 15% (from 201 to 231 syllables per minute; to 241 spm excluding the outlier). However, disfluency markers increased, likely due to heightened anxiety during the higher-stakes graduation exam, with stronger effects among lower performers. Despite the small sample size (n = 7), the findings highlight meaningful improvements in fidelity and fluency, as well as group differences, offering educational implications for English-Korean simultaneous interpreting classes. (International Graduate School of Language Education)