This presentation will describe a longitudinal study examining the performance of a Japanese university English as a roreign language (EFL) program over a 20-year period. Time-series analyses were conducted using TOEFL ITP results for 20 student cohorts to investigate emerging English proficiency trends. The results indicated that specific institutional events, as well as larger population trends impacting Japanese universities, led to gradual shifts in program student demographics, which contributed to changes in proficiency patterns.