Extensive reading (ER) has been documented as a beneficial activity that contributes to the improvement of learners’ English proficiency and reading skills. However, very little research reported the impact of ER on young avid reader’s TOEFL scores. In this talk, I will present my qualitative case study research with a young female avid reader (age 13 and year 9 student) who got a 560 score (58 for structure & written expression; 51 for reading comprehension) of the TOEFL ITP test. Through in-depth two interviews and observation, I found that the prolonged engagement with ER activities since year 3 (from 2016-present) by reading English fiction novels and online Japanese manga has developed her vocabulary mastery, reading skills, and implicit knowledge, which eventually facilitates her to get good scores on the section of structure & written expression and reading comprehension test. This study implies the long-term ER benefits for high-stake test scores with EFL learners.