Drawing on the benefits of Krashen’s comprehension hypothesis (2003) and compelling input hypothesis (2018), Ellis’ “implicit learning without conscious awareness” (2008) and Grabe’s “long-term and large volumes of input” (2009), extensive reading (ER) has been found beneficial to develop the learners' comprehension. This study investigated the impact of extensive reading of two reading sites, BBC English learning and British Council Learning English on high school EFL learners. This study examined if ER facilitated target learners’ lexical and cultural knowledge to develop reading comprehension. Learners of the treatment group (n = 35) and control group (n = 35) received instruction with ER and without ER, respectively, for six months by adopting two International English Language Testing System (IELTS) tests. The mixed-method paradigm triangulated the data to gauge changes in them. The result showed that treatment group learners outperformed the control group, which is statistically significant and implied incorporating the extensive reading as an extra-curricular.