Although research has established that students enrolled in pre-sessional English for academic purposes (EAP) programs make gains in English reading ability, the evidence base for whether gains made during this period of instruction make a difference to future academic outcomes is nonexistent. We report a multi-cohort longitudinal study of a 28-week university-level EAP program that was designed to improve the English language skills of international students in preparation for undergraduate study. The sample comprised N = 405 EAL students who completed the same EAP program in a Canadian university. At the beginning and end of the EAP program students completed a battery of 12 measures, including reading comprehension, reading fluency, and other established component skills of second language reading ability. We investigated whether the change scores of these measures, as markers of skill growth, predicted the post-EAP program undergraduate grade point averages (GPAs) of these same students. The Random Forests nonparametric regression technique was used to estimate the relative importance of all change scores of the reading skill tests, as well as their scores at the beginning of the program. This method identified reading fluency change during the EAP program as a high-ranking predictor of future GPAs. Additional stepwise linear regression modelling confirmed that reading fluency change made unique significant contributions to GPAs in such a way that greater growth in this measure translated into higher GPAs. These findings suggest that reading speed development during an EAP program has a long-term and beneficial impact on the academic flourishing of EALs.