This article reports on a study that examined the effectiveness of an intervention using text messages to enhance the academic vocabulary acquisition of English language learners (ELLs). With a random control trial design, we compared students' learning gain of target vocabulary (direct effect) and its subsequent impact on academic vocabulary learning (transfer effect) with and without the intervention treatment. The study included 108 undergraduate ELLs in a large Canadian university in Ontario. The intervention was aligned with the lesson plans of two comparable content-based courses on English for academic purposes required for the ELLs and aimed at teaching frequently used academic words embedded within the assigned course readings. The results indicated that, with the intervention, students learned significantly more target words. However, there was no difference between the treatment and control groups on academic vocabulary post-test performance measuring the transfer effect. The pedagogical implication of the findings and suggestions for future research are discussed.