This paper examines the role of extensive reading in foreign language learning classrooms. The effects of extensive reading are shown both positive and negative as in Krashen (1999) and Spada (1997), particularly researches done in classroom setting. Extensive reading is hard to implement in foreign language classrooms due to the stringent school curricula despite its benefits in cognitive and affective domain of learners. This study searched 21 papers from research database on extensive reading researches in a classroom setting and synthesized 55 cognitive effects and 11 affective effects from these papers under investigation in a manner of quantifying their means and standard deviations to derive generalizations. Research synthesis in this manner has secured its own status of scientific investigation by providing secondary researchers with replicable methods that produce verifiable findings. The syntheses of researches show that extensive reading is effective in both literacy skills and other language skills such as listening and writing. It also shows positive effects across different age groups, but the effect sizes are different in that elementary and adults gained more positive effects than middle and high school students.