This study aimed to investigate the effectiveness of book reports in learning portfolios in the context of English as a Foreign Language (EFL) education in Korea. Driven by a mixed-methods research design, the study combined quantitative assessments with qualitative feedback to explore the impact of book reports on learners' reading competency and fluency. The study involved 83 participants and the intervention spanned 15 weeks, with the students having access to an extensive selection of 461 graded books available both digitally and in print. The study assessed the impact of book reports on critical reading measures, including TOEIC RC (Test of English for International Communication Reading Comprehension), Accelerated Reader (AR), Reading Speed, and Reading Speed Comprehension. It aimed to identify differences in results between two different teaching approaches: Educator-facilitated and Learner-initiated. In addition to quantitative evaluations, the study integrated input from participants, collected through questionnaires and interviews, to offer a comprehensive perspective on the impact of book reports on enhancing reading ability and fluency. The key findings indicate that book reports significantly enhance reading ability with notable variances observed between the two teaching approaches. The educator-facilitated approach yielded more pronounced improvements, which suggest that the integration of book reports in extensive reading program can be a potent tool in EFL settings, with different methodologies catering to varied learning objectives. By integrating these diverse perspectives, the study result, in terms of implication, aspires to offer insights into the value and impact of book reports, thus contributing to the optimization of learning portfolios for the enhancement of reading skills among EFL learners.