Many educators and researchers believe that extensive reading (ER) is an effective means of improving readers’ performances. This case study aims to investigate the impacts of ER on the English proficiency of two participants: one is a secondary student and the other is a university lecturer. The data were collected from the participants’ journals, IELTS practice scores, and follow-up interviews. The analysis of the findings from different research tools indicated that ER did influence the lecturer’s linguistic and non-linguistic [world] knowledge as well as her teaching motivation. However, the secondary school student did not show significant improvement in her linguistic knowledge of grammar. Both participants were found to maintain their interest in reading extensively on a regular basis. From the results, pedagogical implications were put forward for EFL teachers, educators, and researchers in considering the ages and purposes of ER.