Many research studies into Extensive reading (ER) have recognized its potential for improving language learners' reading proficiency and other language skills. However, some recent reviews of ER research (e.g., Waring & McLean 2015; Nakanishi, 2015; Mori, 2015) have argued for more refinement in research design so that ER research can be more effectively interpreted. Some areas of disconnection include (a) how extensive reading is conceptualized, (b) the lack of long-term studies, and (c) a lack of transparency concerning how much ER was done. Aiming to provide an evaluation of an ER treatment that responds to these three issues, this paper reports on 19 university students who read graded readers on their smartphones for the duration of one academic year (April 2015 to January 2016). Each student read an average of 263,767 words or 39 graded readers during this period. Changes in students' reading proficiency were evaluated in terms of changes in students' TOEIC® IP test scores and scores in the reading section of this test. Results showed that all but two students were able to reach the reading targets and the majority of the student sample were able to achieve an increase in toeic® scores after this treatment.